Hugs Gigi,
So sad to hear what you and your DD are going through.
It's great to hear that you have an appointment for her in the new year, but it doesn't hurt to ask for any help before that!
I also live with someone who talks of suicide often (although in our case it's an adult)
Does it make any difference if you say to her how much you would miss her if she was gone? How you need each other?
A friend of mine had a similar experience with her kids when her marriage ended, but once again they were a bit older. She kept reassuring them just how much she loved/needed/would miss them. It seemed to be better after they saw a psychologist.

Wishing you the best.