If I could go back, I'd tell her not to cry over them. I'd tell her to let it play out, that things will settle into their right places in time, that they will turn into passing faces and people you used to know. 
I'd tell her to speak out, to talk to people about what's worrying her and to get help. I'd tell her to talk to anyone, everyone, (well, maybe not everyone) start conversations, make friends. I'd tell her it was healthy to break off friendships that don't seem healthy for her, that people who force you into things, and laugh when you don't take part in those things, aren't friends. They're acquaintances, like I said - passing faces.
I'd tell her to push herself, to do things she could never imagine doing, to persevere, do something extraordinary. I'd tell her to take photos, find hobbies, collect stuff, to take her mind off of whatever scares her into not doing those things.
Please, God, don't sit there and do nothing. Get out there, organise things, don't wait for people to come to you. Tell your mum you love her, because you're going to lose someone. Ignore yourself when you're angry, but listen to other people when they are - you'll find out a lot either way through anger. Visit your Nan more often and tell her she looks nice today, treasure your Grandad's stories and laugh at his jokes, however unfunny.
I'd tell her not to panic, even though that seems impossible. I'd tell her to be patient, to smile more often and to hold doors open for old people. But I'd really just tell her to do whatever the fuck she wants, because who really cares about the past. Just don't do anything stupid.
i.e. don't play Pokemon Go near lakes, building sites or dual carriageways.
R.
