Understand the whole friend thing.

If you can watch her from afar, when she spins thru this current boyfriend, you may reconsider the friendship. Sounds like she may be on the manic side or do you suspect she's doing street drugs?

If/when she hits the wall & falls into a depression, you could try to get her to hosp & then she would have to be evaluated & hopefully treated.

All this being said, take care of yourself first!!!

Don't know if this helped. Just wanted to respond as this saddened you so.

Best wishes.