Thank you to everyone for your thoughts, which are quite mixed. I have no worries about my DD coping with food etc, she is fairly easy going. She has been away on school trips and short trips with friends and never been homesick, but not for two weeks in a foreign country without us. We are taking a (different) friend away for a week at Easter to Wales, but the girls have been friends since 4 yrs old and we know the parents extremely well.
The girls have had lots of sleepovers at both houses with no problems, we have met the mother a couple of times on the doorstep. The friend is very well mannered, confident and easy going, which I think says a lot about the parents.
There is a younger sister, she's about 8 and I hadn't thought about the potential babysitting element... so I will ask about that! I will also ask about other family members, aunts/uncles etc who she may come into contact with, as well as how they would handle my DD getting homesick or the girls falling out.
I'm sort of relieved that some of you would also be cautious, so I'm not being paranoid! I'm also heartened by some of you advocating the benefits of the experience. (DD is the youngest of three, but the other two are boys... my worries would be different with them, breaking their necks falling out of trees etc!!) NB, my husband is not worried about it at all, so maybe I'm compensating for him!
We are meeting the parents for a meal on Friday night, so I will prepare my list of questions. Thank you all so much.