I do think expectations matter. If a teacher expects more of a child/a group of children, that child/that group of children will (generally) do more. I believe there have been 'experiments' where they grouped children randomly, but told the teachers 'group A are the clever ones' 'group B will need to take it more slowly' etc and after a few weeks already, group A were indeed achieving more on all sorts of measures.
I also think this is part of why summer-borns (on average) achieve less well all through school. Self-fulfilling prophecy. (Not the only reason though).
So from that perspective it does matter.
But the question is, does it matter in the grand scheme? As you say OP this is a 'bad year' so chances are that next year with a new teacher, she'll be moved back to appropriate groups, so in the long term, no harm done.
Personally I do not think you need to teach her extra at home in order to keep up with the top group, to have a chance of moving back to the top group once she's with a different teacher. The top group will not be moving further ahead in the curriculum. What they may be doing is having more 'thinking' questions, problem solving rather than just basic arithmetic e.g.. At that age, though, this won't be putting them ahead in terms of being able to do things the children not in that group can't do. Next school year, hopefully your DD will be able to slot right back in.
What I would pay attention to however is if/how it is affecting her attitude to learning. If she's starting to 'coast', not making any effort because being in middle group is easy and comfy. If she starts to think she mustn't attempt to solve hard questions (as they are reserved for the other table). That kind of stuff, I would address with her, rather than giving her extra work at home.
If there are no long-term effects on her attitude towards learning (and this you can address at home, but not by doing extra work), then no, a year in the 'wrong' ability group won't make any difference in the big picture. Similarly, a very able child who is appropriately placed in the top group, might not every year be appropriately challenged. But again, a year like that won't cause them to fall behind their potential in the long term.