Lucas:
I'm a newbie with Y7 myself - but from what friends say with older children this first term is entirely about settling them in and getting a sense of where they're at as a student.
I can understand you're worried they've put her in a class that will be too difficult - but as you said the assessments were made at the start of Year 6 and I suspect that means she's improved beyond that point during Year 6.
My advice is keep talking with your daughter about whether she's finding classes too easy, just right or too hard. Maybe even jot down some notes on it - so when you have your first parent/ teacher meetings you can raise your concern that your DD is finding math/ science/ etc... too easy/ hard - if that's the case.
In the meantime - just keep a watchful eye on how she's doing and try to avoid helping her too much with homework if she's struggling. Better to turn in an incomplete homework - saying you don't understand how to do this - than have you coach her through the homework and give the teacher(s) the impression she's finding it a breeze.
Most schools offer support for maths at various points in the day (at breaks or after school) - odds are the teacher explained that at the first class. If she's fine in most areas but maybe finds one topic (say fractions or algebra) a bit tricky - she can always come along to a maths support session with her homework and have someone there help her work through it.
In the meantime - if she hasn't mastered her times tables to x12 - now is the time to really get those solidly learned to the point of instant recall.
Great websites for practice:
www.multiplication.com - lots of games to practice times table skills.
resources.woodlands-junior.kent.sch.uk/maths/timestable/index.html - this is the timestable zone of woodland junior school maths zone. Lots of great links to games
HTH