True, there aren't many little girls in preschools or schools these days named
Heather. It's their teachers, otoh, who are named
Heather. It is dated although you're right. The plant is lovely. It's probably one of the prettier flowers/plants used as names.
My perception of
Heather is of a cheerleader (although I've never cheered with any), someone popular, friendly and slightly, slightly ditzy or flighty (blame that on the media, though). I've known several Heathers in real life and some fit this stereotype and some didn't.