She can totally get away with this. There are all sorts of things they can get away with, but as parents, aren't we supposed to be teaching them about socially appropriate behaviour, respecting people, and environments?
The honest truth? I wish I could sit like that at breakfast. I want a chair big enough that I can remain horizonal-ish till about ten in the morning, while someone else brings me smoked salmon and stuff. Some people have it so good.