10 days isn't short notice in my opinion for New Year's. I would have never assumed anything around the holidays. I think you should have asked her plans as soon as November hit.
To a degree, I see your point.
I just feel with the holidays, you HAVE to put some real thought into it. The fact that both are on a Tuesday, it makes sense to me that she'd want to close on the Eve's. But this is something, as a business owner, she should have put more consideration into and made a point to let the parents know WELL before now.
While, sure, the parents could ask her what her plans are if they know they have to work, at the same time, I feel the onus is on her to give them fair warning.