Go and talk to them, go and talk to them!
First of all, your dd needs to sit down and think about what her plans are.
Which A-levels would she like to do? What kind of future has she got in mind? What will that require- e.g. going to university, what kind of university, what are their minimum requirements (easy for her to check online), or if vocational what kind of training?
Then read all the available prospectuses and see what they have to offer. Keep an eye out for all the extras: for instance, do they have links with particular businesses or universities, do they offer enrichment activities that might be useful for her CV.
For instance my own dd (who is quite academic but with a strong interest in drama) decided not to go for the college with the very best academic reputation but for one still has a good overall reputation but is known for its strong drama department and links with that world.
Then she needs to make the most of the open evenings, to make sure she gets to talk to the tutors in her particular area. Encourage her to ask specific questions about what they study, how they support their student's studies and what combinations are allowed (dd rejected one college when she found she would not be able to combine her chosen A-level with a vocational course she also wanted to do). This is also a useful time for asking "what if I do less well than predicted in my GCSE's- how would that bear on my A-level choices?"
She needs to bear in mind that friendship groups will probably change anyway as people develop stronger interests and go down different career paths. But that you can always hold onto your real friends, even if you don't see them every day. So I would advise her to ignore that aspect. Two years from now she will be choosing the university which offers the degree she wants, or the workplace she has trained for, not the one where she will find old friends.