Repeat botox now? Should I do it now before it wears off entirely or wait? What would provide the best result?

Botox should last 3 to 4 months,  12 units is  a very low amount for glabellar area.  Usual treatment is 20 to 25 units with additional on the forehead.  Make sure your provider is using fresh botox and have it injected again about 4 weeks prior to the wedding.  

Thank you for your question Smulv97. I understand your concern. Botox is a purified protein used to address wrinkles associated with facial expression. When injected into the skin Botox will relax the muscles and smoothen out the overlying wrinkles. The most common areas of treatment are in the upper face. These include the horizontal lines seen on the upper forehead when one raises the brows, the vertical lines seen between the brows when one frowns (frown lines), and the crow's feet seen around the eyes when one smiles.
It is difficult to make an assessment without a formal exam in the office where I can view the skin in multiple angles and observe wrinkles formed with facial expression. However, I hope the information provided here is useful.The appearance of frown lines is variable from person to person. Usually they are in a vertical orientation but sometimes they can be oblique and sometimes a horizontal line is seen across the upper portion of the nasal bridge. The most common variation is to have two parallel lines, hence the common term "11's" to describe them. But some people have one, three, or more lines. Some people also will see a bulge in the area when contracting the muscle. This bulge is smoothened out after a Botox treatment.
The pivotal studies used 20 units of Botox in the glabella area between the brow to address the frown lines. These studies demonstrated that the peak results are seen 14 days after the treatment and most people enjoy their results for 3-4 months. At that point, a maintenance treatment is recommended. While some people start to see results as early as the next day, it can take two weeks for full results so patience is important. We have our patients return two weeks after their treatment to assess their results via photographs. At that time additional units may be added if necessary. 
When patients present with concerns about specific wrinkles in the upper face such as the frown lines, I always assess and usually treat the other wrinkles in the upper face including the horizontal forehead wrinkles and crow’s feet. The reason is to maintain a harmonious and natural balance to the appearance of the upper face. The muscles in the glabella which are responsible for the formation of the frown lines serve to pull down on the inner brows when a person frowns. Similarly, the muscles around the eyes which are responsible for the formation of the crow’s feet seen when smiling (orbicularis oculi) are also responsible for pulling down on the brows, but in this case the outer brows. On the other hand, the muscle in the upper forehead which is responsible for the formation of the horizontal forehead wrinkles when a person raises the brows (frontalis) serves to pull the brows upward. If one of these muscles is relaxed with Botox and the others are not, the other muscles will still be active. This will lead to an unbalanced and unnatural appearance of the upper face where the brow can be elevated, depressed, or uneven in shape or position. Therefore, I recommend that my patients take a global approach to the upper face when receiving Botox treatments and treat all three of these areas. Sometimes bunny lines on the bridge of the nose are also treated.
Despite having a natural appearance when performed correctly, many people are afraid of the results of their Botox treatment, in particular before their first treatment, which is natural. In these cases, a lower dose can be used. For example, sometimes I use 10 units in the glabella region instead of the recommended 20 units. In these cases, I advise my patients that the full results will be seen approximately two weeks after the treatment and have them return at that time to take after photographs. At this point, more Botox can be added if further enhancement is desired. I find that when lower doses are used, patients do not enjoy their results for as long; six to eight weeks as compared to three to four months. Therefore maintenance treatments must be performed more frequently.
Botox (onabolutimun toxin) is what we call a neuromodulator. This means that it controls nerves to relax the muscles by preventing them from contracting. Botox is the most popular neuromodulator available, has been the most studied, and is cleared for the most number of indications. Other neuromodulators available in the United States include Dysport (abobolutimun toxin), Xeomin (incobolutimun toxin), and Mybloc (rimabolutimun toxin). Botox, Dysport, and Xeomin are type A toxins while Myobloc is a type B toxin. This means the structure of the protein is slightly different. Overseas many others are also available. Dysport is the most commonly used neuromodulator other than Botox in the United States. The dosing for Dysport is different than that for Botox. Approximately 2.5 to 3 units of Dysport are required for every unit of Botox. For example, in the glabella 20 units of Botox is most commonly used. If Dysport were to be used in this area 50 to 60 units of Dysport would be required. The investment per unit of Dysport is approximately 2.5 to 3 times less than that of Botox. While the manufacturer states that the units of Xeomin are a one to one equivalent of Botox, many doctors find that a higher dose of Xeomin is required to produce the same effects as Botox. Each product has slight differences, but all of them work. Dysport, for example, is known to spread more than Botox. This makes it useful in places like the underarms where it can be used for excessive sweating. However, if it spreads near the eyes it can lead to side effects such as a droopy eyelid. Xeomin is also called a naked protein, because it does not contain the accessory proteins that are included with Botox or Dysport. It is thought to have a slightly faster onset (by one to two days faster) than Botox or Dysport. It is also thought to have a decreased likelihood for allergic reactions, although allergic reactions to Botox and Dysport are incredibly rare. In the United States Myobloc is not FDA cleared for cosmetic use and is primarily used for muscle pain in those with cervical dystonia. The majority of our patients find that they like the results of Botox the best. Additionally, Allergan, the maker of Botox, offers the Brilliant Distinctions Program. This is a rewards program where patients receive points from their Botox treatments which can be used toward discounts at subsequent treatments. Points are also received when patients purchase other treatments in the Allergan portfolio including Juvederm Ultra, Juvederm Ultra Plus, Voluma, Volbella, Vollure, and Kybella or products such as Latisse or Skin Medica products.The investment for a Botox treatment varies from office to office. It depends on the region, office, and injector. The total investment also depends on how much product is required, the areas treated, and the individual. For example, if someone has a larger forehead, a higher dose will be required. If multiple areas such as frown lines and crow’s feet will be treated the investment will be more than that if only a single area is treated. In general, men have stronger muscles than women both on the body and on the face. For this reason, men usually require higher doses than women. Please click the link above for more information. I recommend that patients look for a qualified injector instead of the best price. Look for experience, before and after photographs, and testimonials. The investment range for a Botox treatment is $200 - $500 per area. Areas include frown lines, crow’s feet, etc.
If I had a patient with the concern described here I would want to look at the skin in person. It is not surprising that the lower dose used did not last as long. Ideally I would have started with a dose of 20 units in the area 3-6 months prior to the wedding. This will allow me to gauge the effect and adjust the dose if necessary before the wedding. At this time I would say a dose of 20 units approximately two months before the wedding would be appropriate.With any injection, there are risks such as pain, bleeding, bruising, redness, swelling, tenderness, and infection. We take special precautions to minimize these risks such as using a painless technique. We also treat bruises with a laser as early as the next day. Bruises usually resolve within two weeks if untreated. After a laser treatment bruises usually resolve in 1-3 days, but may still take two weeks for full resolution. In addition to these risks, with Botox there is also a risk that the product spreads or diffuses to nearby structures. Spread to nearby muscles can lead to side effects such as the temporary appearance of droopy eyelids or a temporary asymmetric smile.

After a Botox treatment, I recommend that my patients avoid heat exposure, alcohol consumption, and strenuous exercise for 24 hours and not lie down flat for four hours. This is because all of these activities may possibly lead to the movement of the product and consequent side effects such as droopy eyelids. Although there have been no definitive studies shown that these actually occur and some physicians do not provide such aftercare instructions, in the absence of data I err on the side of caution and recommend that my patients avoid such activities.

Please consult with a doctor for specific recommendations. Good luck!