Welcome EscaMac. Similar situation with DD1, did slightly better than expected at GCSE without too much effort. Then a combination of not listening to advice on how big the leap to AS was, a bad subject choice that she refused to drop early on and not taking well to independent learning. Also, has a weak area in her Uni subject which is compulsory at AS only So also ended up with a U for 4th AS, being a grade down in 2 and 2 grades down in the 3rd. Fortunately, with large discrepancies between modules, only resat 2 where she felt she could gain the most marks. Don't think A2 work has been hugely better for her, but she certainly put in more revision than last year. Also had a great PS, predictions 2 grades in total above her AS results, got all 5 offers which were mostly a grade in total above predictions.
So keeping everything crossed that she hits her firm choice, knows they generally allow a drop, but maybe not 2 grades, and maybe not a D in her 3rd subject, being an RG Uni. In her favour is that it's not the most competitive of subjects, and she has been offered a music performance scholarship there which may carry some weight.
It sounds like your DD has been very focussed this year. Good luck - at least only 2 weeks left to go. Is it a very competitive course she has applied for? Does she have a plan B?