How to tell my MIL that I dont want my DD leaving me overnight yet.

[black_rose]

I wouldn't want my kids on a plane with a 15yo or that far away either, just keep saying no. Doesn't matter if the rest of the family are happy to do it you are not and that's all that should matter.

[Rivlas]

I agree with the others who have said to build up time away.

What is going to happen if she get really upset and wants her Mum. You are not just around the corner and I know you certainly don't want a phone call with a distressed child on the other end wanting to come home.
When you do let her go overnight/away you want it to be a fun experience, not one where if she will gets homesick to never want to go away again.

Just say no and leave it at that. Remember, you are the parent, we as grandparents need to learn to respect decisions made by the parents