How far away is she ? If it was a short drive perhaps you could pop over with something she has "forgotten", it is a hard one, keeping them happy vs them getting on with it.
I'd be tempted if it was not far to pop in a cake that she could share, plus forgotten item, she could then use the cake as an ice breaker, as a reason to knock on other's doors. It may be that by seeing you she feels happier and then she might be less home sick. I agree it is a really tricky one.
I was talking to a friend whose son went last year and she said the second week was definitely hardest for her son. I suspect by the second week the novelty has started to wear off and they are all feeling a bit tired and missing home.
My dd does not go until next week and so apologies that I can't offer any first hand advice.