I'm skeptical - is her brother so demented that he's going to claim she wasn't there despite every other guest easily able to testify to the contrary, if she was?

And is that her only receipt as proof, mommy looking beautiful in her casket and a fist fight, both of which she could have easoly found out from other attendees?

It sounds like a case of lost in translation - she was probably there in some form but not in the way Tommy would consider really being there.