Can't help on the problem, but can say that one day, for no apparent reason, your daughter will probably turn the corner and start to get her life back together. She may need to "jolt" herself with something, because depression can be very self destrutive, and it is only by the person realising that something has to change, and making that change, that things start to get better. The good news is that after an experience like that, you can become stronger.
Going back a few years, I was facing the iminent death of my mum - I knew it was on the cards, and soon, but didn't know when. One of my dogs then died, then a month later so did the other one - only dogs I know but part of the family for 15 years. Six weeks after that, my mum DID die, and after the funeral, my sister and her family stopped talking to me - why I don't know. I still had my girlfriend, on and off for 3 years but mainly on, who subsequently moved in with me, but that too ended just a few months later as a result of money problems - in a nutshell she had kids (who weren't living with her) and she threw money she didn't have at them, trying to make them love her more than the dad. Long story short, she got into incredible debt, so much so that unless things changed, my house would be put at risk.
Anyway, she went, so in the space of 4 months, I lost everything that mattered to me and ended up very very depressed for months,
Anti depressants CAN help more than you think, so please suggest she gives them another try, and from there do something else to help buck the downward spiral - join a club, help out somewhere, do anything just to get a bit of self esteem and control back.