No, but rename buffy to buffy-the-vampire-slayer, the proper full name of the franchise.
I don't think we need a character tag for Buffy herself.†
So the question now is, what tags do we need?
The Buffyverse consists of Buffy the Vampire Slayer, which has a movie, a TV series, a line of comics and a line of novels, and of Angel, which has a TV series and a line of comics.
So we have two tags for two TV series and their accompanying works. For questions spanning the entire Buffyverse, just add both.
I think that we could rename buffy to the full title, buffy-the-vampire-slayer, with buffy a synonym.
But that's a bit besides the point.
†: I know there's a certain high-rep user who is a big fan of the character, but I still don't think we need a character tag for her. Sorry, Richard.