....... parents can't ALWAYS be held responsible for childrens' behaviour, however they can't NOT be a contributory factor.
Summer, I feel I must stand by what I've said here but this is in no way saying that everthing parents contribute is bad. Parents ARE responsible until children reach a certain age because they can't be expected to be responsible for themselves but there comes a point when they/we must take responsibility for ourselves.
I'm so sorry that you're having such a difficult time and I hope there's somebody you can talk to when the stress gets too much. Coping with someone with depression, I imagine feels like treading on eggshells. You must feel wrung out at times.
I feel certain that it will have been suggested to you already but is it possible that your daughter abuses you because you are the safest person she knows?
I hope that, in time, things will improve.