Slightly contrarian view, though I do see the logic above. I'd simply ask for her to be placed with kids of her own grade - where the education system has deemed she learns best. I've got no evidence for this, but personally that feels more neutral/ evidence-based, rather than asking for special favours to ignore the age requirements. My experience has been that most activities get tons of requests to ignore age limits - and most of them are spurious. But when I talk placement needs instead, I get a different response. For instance, your science camp said 14, but my 12 year old can totally handle it - that gets me nowhere. But, if I say my 12-year old has his grade 9 math credit and has done these high-school-oriented science courses, and so is ready to learn the same material as the rest of your group - that gets him in.
How much capital to expend on this battle depends on its impact. You are starting off on a major move and a lot of demands for serious adapting. If placement with the younger kids is going to get your DD off on a really bad foot that may flavour her view of the whole move, then it's a battle worth a little energy. (I suspect your younger DD might fall in the latter category.) So maybe try something apologetic but unequivocal, like, "Sorry, I should have been more clear. Both girls are in grade 7 and should be placed with the group that includes the grade 7s".
