I'm assuming that this incident was in Your home and that the others are living there with you. If that is the case, you need to set up ground rules, such as: no violence, no abusive language, no put downs, etc...you get the idea? Present this to both your daughter and your girlfriend that you will not live in a house that is not peaceful and respectful and give them the list of rules. They must agree to abide with them or they will have to live somewhere else. And enforce it every time.

This is what I had to do in my house so that I could have peace. It took awhile and they "tested the waters." But, when they saw I wasn't going to budge on my rules, they complied. It forced them to grow up and act like adults. Society does not permit violent behavior, abusive talk and degradation. So, ask yourself why should you either?

At first, for you it will be tough because you will feel guilty and want to back down but stand fast and force them to come UP to your standards of behavior in Your house. In the long run, you are really doing them a favor by not accepting their bad behavior.

Also, it sounds like your daughter needs to see a physician to determine if she needs to be on medication or some kind of treatment. Death wishes are not normal. Also, is your daughter doing drugs? Moodiness like this can be a sign of drug use.

My 2 cents worth. It worked for me.