Just recently I've changed my approach towards my depressed son and have opted for the "less is more" approach. I find that by giving in too much to cater for him actually makes the situation worse - it's like feeding a dependancy syndrome. The more I do and the more I dance around his needs to ensure that he is safe and happy, the worse he becomes IMO and the more frazzled I become. Taking a step back and trying to get the "adult" part of them to function and strengthen is what we should be aiming for. So instead of positively reinforcing their fears and depression, focus on weakening them by getting them to gently face those fears and gain confidence in themselves. I know how hard it is to deal with a depressed teenager - it's almost as if you're damned if you do and damned if you don't. At the end of the day our children need to take responsibility for themselves and somehow learn to manage themselves (depression and all). The only way we can let that part grow is to loosen our innate protective and nurturing instincts which tend to go above and beyond normal because we are trying to ease their pain and suffering.
When you say "if anything bad were to happen to her", I'm assuming that your greatest concern for her is her safety from self-harm/suicide. Have you considered making a safety plan/contract with your daughter which would include her guaranteeing you that she remain safe until you return home and for her to contact you if she feels unsafe? Have you done a risk assessment on her in terms of suicidality?
You can find such risk assessments online via several websites.
Here's a few links you may find useful
https://www.suicidecallbackservice.org.au/concerned-about-someone/suicide-warning-signs
https://www.suicidecallbackservice.org.au/concerned-about-someone/helping-someone-to-create-a-safety-plan
At the end of the day your well-being is as important as hers and investing in some self-care and/or trying to live beyond the constraints of caring for her is NOT selfish.
I'm happy to hear that she is going back into hospital soon - not only for her, but for you as well.
Take care
Janna ❤️