Expecting teenage girl to share room with teenage boy

[clearlyaplasticgnome]

My sister, and her 15 year old daughter have been invited to stay with friends in Edinburgh next weekend. My sister has just found out that her friend is assuming that 15 year old daughter will be happy to share with friend's 16 year old son.
My sister is shocked, and so am I.
AIBU to have told her to just make up some excuse and not go? My sister doesn't know what to do.

If there are bunk beds in the sons room I can just about see why the boy's mother would suggest it, but it still isn't acceptable.

Suggest that either the friend shares with her DS or your sister takes an airbed and sleeping bag with her for DD as she wouldn't want to share with a teenage boy.

Some parents don't really get that they don't have toddlers anymore.

I have now suggested to my sister that she go back to the friend, say her daughter is at a self conscious age, and could she just bring a pillow and duvet into the sitting room at night and sleep on the floor.
I'm waiting for her to get back to me.

Waiting for my sister to get back to me, I mean.

That sounds like a good suggestion, clearly. FWIW I've slept on a two seater and I'm 5'8" so she might not have to sleep on the floor, depending on how much she likes to stretch out!

Sister is going to message friend now with that suggestion. Will let you know how she got on.

Upshot is that friend wouldn't hear of my niece sleeping on the floor and has offered up her room to my sister and niece.