You are in a difficult position. You should not feel guilty for the way you feel. Who would not feel better with less stress? I hope you can find a way to deal with this situation. I know it is weighing heavy on you. I guess you just have to have faith that things will work out. It is a touchy subject when dealing with someone else's child.
Try and enjoy your day and not worry so much about it, easier said than done.
Maybe the three of you could get some counseling? If the daughter is not willing to open up though................
I really believe teenagers watch so much crap on TV, all the trauma and drama, that it kind of warps their relationship with reality. Just a theory.
Send good vibes your way.