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As a teacher of teenagers, and having been on lots of residential school trips, I'd say you have nothing to worry about. Girls will change their BF countless times, have arguments, get back together time and time again. It's all very traumatic for them at the time, but part and parcel of their journey. I'm not sure what you mean by 'is there anything she needs to know' but if it's in relation to how the friendships will be 'managed' on the trips I have done, pupils are asked in advance who they want to share rooms with, usually in groups of around 4, and teachers are very good at knowing who gets along with who. If you or you DD are worried, simply speak to the teacher organising the trip. They will have done this countless times, and will be able to sort out most things. I am yet to go on a trip where I haven't had to talk to a group if girls about tension in a group, but within a few hours of a chat, they are all best friends again.
Hope I've helped. If I've gone off at a tangent, just say.
Don't know where to put this, but she's going to France for 6 days on Thursday. Is there anything you think she needs to know? She is 13 and this was booked start of Y7 when she was best friends with let's call her G now she still likes G but has a new best friend L???