I don't know TONS on the subject but in MY own personal experience with a friend who was bi polar and acted like SYBIL most times, I found that I usually just had to ride the wave out... I stayed up late nights with her and listened whenever she needed to talk about whatever she wanted. Believe me..the conversations we had were erratic often times... When she wasn't manic it was easier to explain to her what is going on...she decided,in one of her alert and in control stages she got back on her medication and although there are side effects it ultimately made a world of difference in her quality of life.
Psychosis can accompany depression, not just mania. I've had it happen both ways, though for me, it's far more common in a mixed episode or a manic episode. Each person is a little different. What behaviormakes you view her as being psychotic/delusional?
Personally, with what limited a glimpse I am provided by your post, I would continue to communicate with her as though she's perfectly fine for now. If an opportunity arises in conversation, take it and gently ask if she is ok. Don't ask, "How are you?" Look her point blank an ask, "Are you ok?"
Why? There's something about those three little words. "How are you?" is easy to lie to. We all tend to do it every day, saying we're "fine" when in fact we're ok or a bit stressed or this or that. But "Are you ok?" I don't know. I've found it difficult to say, "Yes," to. It's like it penetrates through that mask somehow.