I am so sorry to hear this, I wish there was something I can say or share with you, but sadly I do not know.
Has any of her docs try antipsychotics, and mood stabilizers?
Sounds like she is in more of a psychotic state at this time, bipolar is not a "one size fits all" sort of thing, for example my oldest and closest brother was DXed back in the 60's as schizophrenic, the US back then used that disorder as a "catch all", after treatment for that disorder wasn't the route to go, another pdoc (bless this man) who had studied Psychiatry, and was also a professor at his university in Italy, had recently been in the US, and started his practice here, helped my brother, properly DXing him, as bipolar-I, back then called manic depression,
well to make the long story short (hard to do) lithium was the only med that helped him, and it had been back then newly released in the US, even though other countries had been using it for years previous. Before that, many meds were tried and failed, (and there were less kinds too)today fortunately there are more and newer meds. perhaps your sister was misdiagnosed or needs a change in meds. the hard thing is to convince her to be compliant, that is frustrating.
When and if that hurdle is accomplished the rest may go easier, till then I wish you lots of luck and love with this rough time in your life as well as hers.
Please take care,

DE

BTW
I was DXed as bipolar-II (mild) II's have more serious depressive episodes than I's but much milder manic or hypo manic episodes. There are so many variations and combinations of this disorder, one can be bipolar and also have other disorders too, I was also DXed in addition to bipolar, ADD (mild), hell, I seriously feel the ADD is more of my problem, but my pdoc won't treat me for it, he thinks it isn't as serious as others having that, I told him, "oh yeah?" "come and spend a day with me, you'll see", ha!ha!
But I am seriously going to work on him to at least give treatment a try, if not there are many other pdocs out there. Keep that in mind too, sometimes we need several pdocs opinions, when nothing seems to be working.
Just my 2 cents on that.