It sounds as though te lady was rude in how she asked, but it isn't a rude request in itself, and unless I am missing something in the OP, at the time this person made the request, she would not necessarily have known that it wasn't possible.
It's not usual where I live to have an open casket or a formal viewing/visitation but it'soften possible for people to visit the funeral home to say goodbye if they wish.
of course the lady should have asked whether it was possible, rather than framing it as "I want" but it's the tone which is rude, not the request.
Of course the family's wishes are paramount, but it doesn't sound as though the lady would have had any way of knowing what the families wishes were, in advance of asking.