Big breath in Scarlett, if she suffers from depression she may well be lashing out and you are in the firing line, as you are part of her 'credible' base to which she can relate.
In many ways, IT IS NOT HER, her real personality being masked by the depression.
IT HURTs, but if you are a true friend to her and she to you in the past, hold in there.
I've been there, seeing a close friend sectioned after a lot of what you have described and more.......you are the sane one, she needs your love, but it has to be a measured way to what is going on. What about others in her family - talk to them, share your concern and love and what can you do to stabilise her and bring 'improvement' to her life - often those friends have no idea of how she is behaving outside the family - or in helping to pick up on the warning signs.
Good luck.