I feel your dd should have been flagged up for not improving much over a long period of time. But because of the change of school she may have been forgotten about. I think you really need to have a meeting with them to find out how they intend to help your child reach her predicted levels and ask what topics they will be covering this year so you can support her at home or if you can afford it use a tutor or group tutor session.
My dd was a 2a at maths in year2 and was a level 3c at the end of year 4! Not much movement there! I worked with her year 5 teacher to get her to a level 4b by the end of year 5, so it can be done. Good luck