I'm sorry to hear your sister is having to deal with this. I'm proud to see you supporting her so much though. Not all of us with PMDD have such a support structure. You mentioned she's on medications for most of her mental health problems. I'm assuming she may have other issues then aside from PMDD? It's a very blurred line when other conditions are involved. She should speak to a doctor and confirm whether she truly has PMDD. Many many other mental conditions can be exaccerbated during the same time PMDD would occur and show the same symptoms but it's actually just the same conditions the person already has on overdrive. Usually upping the medication for the condition during that time can help.
If she doesn't have any other conditions or is sure it's PMDD- and Prozac has not worked, I'd recommend Yaz as long as it's safe for her to use. Vitamin regimens often help with some of the mental and physical side effects. St Johns Wort can be helpful as well as 5-HTP with emotional issues, but interacts with many other vitamins so take caution with that and research first. They cannot be taken with any SSRI's either.
Nearly every woman I know admits exercise and diet, sometime unfortunately when you aren't into that kind of thing or find it difficult to control, are very helpful when changed to suit the course of PMDD. The Paleo diet is heard about the most. While PMDD makes us crave sweets and carbs often, those are the thing that make it worse. Carb cravings should be soothed with complex carbohydrates, not chips, etc. Choose sweets such as honey, fruits, and dark chocolate in moderation. Fiber and protein are important for energy.
Aside from such, if your sister is done bearing children or does not wish to, removal of her ovaries is an option. It would put her into medical menopause, but PMDD would also be over. Some women actually do opt for this radical treatment. Keep in mind PMDD will only worsen with age and pregnancies. It is best to seek treatment now before it is even more out of control.
Unfortunately, I know nothing about Texas dr's. One good thing is that PMDD is now being upgraded in the DSM-V to an actual mood disorder. With this will bring more recognition, awareness, and perhaps more treatment options. If she is interested in pharmaceutical medication (which seems to be the most widely effective thus far, hence why most women try that first)- she can seek the help of a gyno or psychiatrist. Simply calling the dr's offices and asking the nurse or receptionist if the dr is familiar with PMDD will work just fine. You aren't likely to find some sort of expert- because there are none yet. The experts are us- women like me, and your sister someday very likely if she so pursues further education on PMDD for herself. If she is interested in more natural treatments, look for homeopathic healers, internists and naturopaths.
If your sister has Facebook, tell her to look up PMDD Support 2 in Facebook groups. The moderator's name is Cat. The symbol for the group is a green apple. There she will fine women just like her, every single day, helping each other to feel not so alone and a little bit- normal. Good luck to you.