As a woman can I safely use 5% Rogaine foam twice a day?

This may be possible, but I suggest seeing a hair loss expert now to evaluate and go over your condition and provide you information about your best treatment options. There are great non-invasive options like prp/progesterone and/or hair transplantation. See an expert. Best, Dr. Emer
 

As an Integrative and Regenerative Medicine practitioner I'm always cautious of big pharma solutions to treating the symptoms of any condition or disease. 
Big pharma solutions certainly have their place. However, they should only be utilized when truly appropriate. Something that works for the shorter term all too often should not be considered safe over the longer term.
It is also very important to understand the root cause of any condition or illness whenever possible. Simply treating the symptoms will not fix the root issue. Therefore, if only symptoms are treated the root issue is left to worsen, this in many cases will lead at best to the need of increasing medications to possibly unsafe levels. 
At worst and all too frequently, when the root issue is not treated it can also lead to other problems being triggered. Of which may be compounded by the medications used to treat the symptoms in the first place. 
At that point, mysterious health issues can arise leaving you and your physician with a complex puzzle to unravel. 
I sincerely recommend finding a good Integrative or Functional Medicine physician that will identify and treat your root issues. Once this is accomplished, you and your doctor can address all other alternatives to regaining your hair as well as strengthening what you have. There are many for hair loss today that are absent possible adverse side effects. 
A great jump start on things may simply be PRP Hair Regeneration or one of the more powerful variants of it. 
Also keep in mind that just because the issue may be a genetic it doesn't mean we can't safely override that genetic trigger today. 
Wishing you a great outcome to your hair loss and a healthy life. 
Warmly,
Arbella Sarkis, MD 

If you are not getting side effects such as dizziness, headaches, swelling in the ankles, excessive hair growth on the face, heart palpitations or any other side effects then yes, it may be possible for some to use twice daily. You'll always want to review this with your physician and team. For some patients a reduction in the dose of minoxidil like you have done leads to hair loss. 

Minoxidil is safe to use for women. Topical use is much safer than oral use of minoxidil for hair restoration.

Females with hair loss who are premenopausal should not be using finasteride because of the risk of pregnancy. Minoxidil is fine at the 5% concentration