Did has just started yr 9. She's reasonably bright and works reasonably hard, she goes to a good comp which gets pretty good results.
She's quite arty and loves English, history and science. Maths has always been her worst subject although she has managed to get OK results. She finished yr 6 with a 4a which we were quite happy with and has been in set 2 (of 4) in yr 7 & 8 where she felt she was around the middle of the set ability wise and managed quite well and gained confidence although maths was still her least favourite subject. She finished yr 8 on a 6c which was good for her and she was quite surprised by.
The school have restructured the sets this year so there are now 5 sets. Dd has been placed in the second set and she now feels that she is at the bottom of the group and struggling to keep up with the rest of the class. She got quite upset doing her homework yesterday as she didn't fully understand what she had been doing in the lessons 
I've told her to talk to her teacher and tell her that she's finding the work difficult. I don't want her to lose confidence as she's done so well to improve and she liked being able to feel like she could do well last year.
Would it be reasonable to ask the school to drop her down a set? I suppose they are looking at her improvement and thinking she may be capable of A/A* (gove level equivalent) if they push her a bit harder but I worry it might have the opposite effect.