I agree with kraftiekortie. I have faced a lot of that kind of things with my girlfriend. The problem is not something obvious you are missing, it is unfortunately context-dependant and person-dependant, and unless we miss some unwritten rules that are specific to that family, I think it likely has more to do with your girlfriend and her relationship with you (and possibly your daughter) than with anything being inherently socially unacceptable.
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ouroboros
A bit obsessed with vocabulary, semantics and using the right words. Sorry if it is a concern. It's the way I think, I am not hair-splitting or attacking you.