I know people who have good results using the Alpha Stim for stabilizing mood imbalances. A friend of my daughter's uses it for her bi-polar disorder and finds it very helpful. My daughter uses the alpha-stim to deal with brain chemistry imbalances from her car accident last year, and finds it very helpful most of the time.
Might check it out. Here's one link about it:
http://www.alpha-stim.com/SCS.html
I believe you need a doctor's prescription for it, and that some psychiatrists and M.D.s are more familiar with this non-drug approach to balancing the brain than others -- so if this approach interests you, do your research and present it to your sister's practitioner.
BTW, my daughter got her alpha stim used on Craigs list . . . she did have a prescription for its use, but had she not, she likely would have tried it anyway, as she prefers non-chemical approaches to health care.

Hope things improve for your sister. !
Suz