Despite what most young people now believe, the word "Betty" never had anything to do with hotness. It started in the 80's and simply means a girl who skates, a girl who surfs, or any girl who does something that the boys are doing. Betties are cool, but aren't necessarily attractive.
Word evolution is okay, except when it comes out of ignorance, and you end up losing a really great word.
They still haven't torn up that old church pool we used to go to; tonight we're going bring a flood light and some 40's and skate it for a few hours. This betty we know might show up and bring a couple of her friends.