I was educated overseas at an international school which I think followed a more American-style curriculum. I was really behind in maths when I got back to the UK. I was about the same age as your daughter.
The school had not given me a thorough grounding in maths facts, especially things like tables, or sufficient practice with basic algorithms.
How are her tables etc.? Number bonds? Is she quick and fluent with the absolute basics?
Like pretty much everyone in this thread, I recommend getting a tutor. Sad to say this, but you are probably pissing into the wind if you are trying to get help from school--right now state schools don't have money for helping even children with profound difficulties, let alone kids who just need some extra work.
You will also need to do extensive work with her yourself at home. A tutor once or twice a week is not enough in themselves. A tutor can explain difficult concepts to her, level-check her, give you an idea of what to focus on and provide support and encouragement, but it is likely that she needs lots and lots of practice to build speed and automaticity, and this means doing some work daily. Get some workbooks and do practice with her daily, of whatever the tutor thinks she needs help with. Try the Singapore Math workbooks, Saxon Math or Kumon.
Be prepared to be firm if you get resistance from her--bribe her a bit if necessary in the early stages if it all feels like you are wading through mud.
And the golden rule is: fluency with the absolute basics builds competency in the next stage. If you are so quick with your tables that you can remember them like a snap of your fingers, it means that that is one less thing you will have to think about when you are doing, say, a fraction that involves a multiplication table--so you have more room in your brain for thinking about the other aspects of the fraction problem.
And don't lose heart. I started back in the UK at age 9 very behind my peers. By the end of Y7, after putting in some hard work with my parents and at school, I and my best friend basically tied for top place in every class maths test. I went on to get good maths qualifications and go to an excellent university. I'm so glad my parents sat down and did the work I needed to help me catch up.