Freckles on 13yr Old?

In this situation, I would highly recommend that she wear an effective sunblock.  Although there is no reason why she can't have IPL treatment, it is my recommendation that she wait until she is older to do this.

To best minimize freckles, avoid or protect from the sun using a broad-brimmed hat, large sunglasses, and a good quality sunscreen or sunblock. IPL can be considered, though she is a bit young  - that said, if she is quite disturbed by it and can tolerate the discomfort, IPL would be a reasonable treatment option. ~Dr. Benjamin Barankin, Toronto Dermatology Centre.

Her best friend will be an effective sunblock.  Preferably a mineral based SPF (Zinc and Titanium Dioxide) as they reflect the rays away from the skin vs absorbing the UVA/UVB rays.  A good one is Biopelle Up the Anti.  In addition, I might suggest checking out a good mineral powder that she can apply throughout the day to boost her protection.  This protection will be a committment if she wants to see her freckles lessen.  There is no reason she can't have IPL to help break those freckles up and speed up the process.  She will likely need approximately 3 treatments at 3-4 week intervals. 

Freckles will not go away on their own and you should be sure that your daughter is wearing a broad-spectrum SPF every day, rain or shine.  If not, she will continue to see more freckles as time goes on.  A good one for teens that doesn't feel greasy and won't cause breakouts is Neutrogena "Clear Face" SPF.

As far as having IPL treatments, there is no medical reason why she can't have them (you will have to be present and sign her consent for treatment because she is under 18), however, these treatments are not exactly comfortable and might be a bit scary for someone her age.  If she decides to go through with it, she will likely need at least 3-6 treatments, 3 weeks apart.

Topical creams can lighten freckles, but take a long time to see results (1-3 months).  A 4% hydroquinone cream is typically prescribed, but many of the new OTC "skin brighteners" with Vitamin C, Arbutin, Kojic Acid, etc. can also be effective and are often gentler on the skin.  Again, daily SPF is especially a must when using such topicals.