S.W.
Yes. By now she's lost a lot of teeth, and has several more to go... I would've just been glad they remembered to make a deal about it. This tooth fairy has been guilty of forgetting a time or two.
I really would let it go. There will be MANY parenting moments, this is just one small one. If you are OK with being gone and leaving her with the in-laws, then don't be resentful that they got to "parent" her for a couple of days. Isn't that what you asked them to do?