I still think discipline is very important. Depression should not be an excuse to be abusive, (I'm not even sure why it would be, tbh) and I'd be concerned that letting her getting away with it repeatedly would only serve to teach her it's okay. It sounds more like other issues are going on to cause that sort of repeated outbursts. Sorry if I sound insensitive--I'm typing against the clock here at 2:42am with someone wanting me. Hah Take care and good luck to you and your daughter.

Also, remember to look after #1 as well; this is very important when trying to support someone else with mental health difficulties.