Have you tried approaching some of the other girls and seeing if there was some way the group could do something nice for her like take her out, make her dinner, send flowers etc.?
I don't know if the sister is religious but perhaps going to church together might be a nice thing to do...or seeing if she'd like to talk to someone about everything. It's SO hard to say what is the best thing to do. Some people want privacy and others need to talk about things to feel better. Whatever the case a simple acknoledge the problems and reassure her you all will be there.
I'm so sorry to hear about this...I'll be praying for her.
Hootie
