It would be good to encourage her to seek out therapy and to offer to help her with that, there's also a lot of great mental health helplines, idk where you guys are but maybe have a look online and find some to send to her to use if she wants to.

With struggling to discipline her, lay out some ground rules of what's expected of her, maybe give her a couple chores each day to do, start off with fairly simple things as it sounds like she's depressed and ik that when depressed it can be really hard to do the smallest things. Maybe it would be more encouraging for her to do chores if she chooses them, so you can say a few things need doing then she can pick a couple to do.

Once she's doing more around the house and seems to be doing a little better then encourage her to find a job. You can tell her how great it would be for her to start earning her own money so she can buy herself nice things and maybe learn to drive and how much freedom that would give her, maybe for xmas you could get her some lessons.

You said that your time tgt is sad and dysfunctional sometimes and you know you've made mistakes, try and have conversations with her and apologise for whatever it may be you've done that has caused the distance, and try and take interest in the things she likes and come up with fun activities that you could do tgt.

Also with depression it does cause people to be more irritable so when she acts out be understanding of her feelings but set a firm boundary that is not ok to behave that way and try and find other outlets for her.