Agree with this. My DS’s college has an algorythm which suggested in his first week of college Y12 that his grades (the same as OP’s DD) would predict CCD in A Levels. On this basis - ie the fact that he WOULD get A Levels - he was allowed to proceed. By December his end of topic tests moved him to BBC and by Easter they were confident he’d get BBB - enough to get into most mid level unis and/or a foundation year at even a Russell Group uni. He worked his socks off, did every assignment with 100% commitment and focus, and has managed for the first time in his academic history achieved 100% attendance. He goes to lunch time clinics, takes the advice to read around the topic (teachers happily give recommended reading lists).
I haven’t had a chance to look back through OP’s posts, but to this day we have no idea why my DS did fine in mocks (predicted 7-9s) and flopped a bit in exams and we can only assume it was a mix of nerves, stress, overwhelm at the sheer number and lengthy period of examination, perhaps combined with a bit of overconfidence. It’s a snap shot and not definitive, as my own DS’s subsequent AAB in AS Levels this year reveals.
If DD is otherwise really bright and had good mocks etc, then I’d sit down with her and make sure she really wants to do A Levels and is genuinely interested in the subjects she has been offered. I would then invest in a tutor to go through exam and revision technique, even if you just have one block of 10 sessions mid y12, to make sure she really understands what she may have done wrong or how she could improve. If there is no back story of struggling with grades in Y10/11 and she is 100% committed, there is no reason she can’t pull off BBB+ with the right support at home and school/college.
Re RG unis - please do as others suggest and talk to her about the fact that it is a self-selecting club. Yes, they are great unis, but Bath, Loughborough etc are all brilliant universities, too, who chose not to join. She should be looking at which subjects she is truly interested in to devote 3 years to and then look at the modules available. If the best courses include a couple of RG unis, and she is getting the grades by the end of Y12, great - but it’s not the best all and end all.