I spoke to you on your other thread. I agree she is around 2 years behind. This could be due to SEN, but also could be due to different schooling systems, language, school moves, and poor early care.
If you can get hold of level descriptors for English and maths, you can see for yourself (or maybe the school will do it for you) whether there are any earlier gaps. Especially with maths it is very additive, if you don't get the foundations right it is difficult to build on from there.
If care has been lacking, you can help in maths by doing lots of playing with ADD, eg building blocks, cooking, pouring water into different containers etc. Really making sure the pre-school foundations are there. When my eldest ADD arrived age 8, she had missed out on much early playing, and did not know for example that the heavy side of scales was the lowest side.
Although it is difficult, try not to get too caught up with where she 'ought' to be by end y3. There is no point pushing her on Y3 stuff is she hasn't got the y2 skills yet.
It is possible, over time to catch up, but it is a long slog. My ADD1 was a 2a in maths end y4 (1.5 years behind), reached 4b end y6 (ie caught up).
NB . None of this is as important as making her feel secure. She won't learn if she is on edge the whole time.
Also have a look on the adoption board here (under Becoming a Parent) and also at the Adoption UK site, which has loads of information on things like settling new ones, kinship care, education issues etc.