Kid is 13.
My take is, we agreed to the rules when we signed up, now they've changed the rules. Legalese fine print probably means they keep my money whether the kid goes on the trip or not, but "doing the right thing" to me means if they can't honor it as it was agreed-to, we should have the option of undoing it and getting a refund.
We've discussed with kiddo, she's in the "OK, I'll just get the vax" camp. So probably a moot point. I remain philosophically opposed to the mandate side of it, but the libertarian in me says she's mature enough to make her own decisions on many things, this being one of those. I'm also aware that if we want into Europe within the short-term-forseeable-future, vax is going to be required for that as well.