You're right; it is my problem and not hers.
There won't be anyone home when she goes home, so it's not about coming back to family, purely a financial choice for her.
She does know I'm disappointed, and has said she will think about it over this week, but I almost don't feel fussed about it anymore, just disappointed.
I think part of the reason it affected me the way it did was the way she told me, too. Like I didn't factor in at all, and she seemed almost surprised when I commented that it would impact my plans.
Ah well, it's only one night, just means I'll have to change my expectations.
Thanks all