Hope the rest of your girls do fine and give you lots of eggs. They do tend to get into habits don't they, it is amazing how much personality they have as individuals. Were you feeding them layer food, or did you just have oyster shell on the side for them?
Sorry to hear about your girl. As long as your other girls are acting fine and seem OK, it was probably just a problem with the individual pullet. Like older girls, sometimes the girls that are just getting ready to lay will have problems and wind up with internal laying or peritonitis etc...