Many times I meet reasonably smart children who has coasted through their early maths education, able to rely on their natural ability, without needing to make too much effort. As they go up each academic year, the subject gets more difficult and there will come a time when their natural ability is just not good enough. They become disheartened, they no longer get the praise they used to get, they even start to get criticised, they lose self-confidence, they fall behind (a particular problem in maths), they develop a grumpy attitude, become disruptive in class, fight with the teacher and it all goes downhill from there.
What your daughter needs to do is change the way she does school because her current method of working may no longer good enough. It is harmful to just tell her to “work harder”. You need to encourage her to “work cleverer” which will mean that she will have to do things off her own initiative instead of only doing the work her teacher tells her to do. She will have to accept responsibility for her own effort and success.
That will be a frightening change for her and she will need your support while she develops her new skills, regains her self confidence and catches up on her maths. This is what I do as a tutor.