Raven knew Beast Boy for years and she either was ever annoyed by him or just tolerated him. Raven only tolerates Beast Boy as a teammate, I don't think she would even call him a friend. Raven, meanwhile, was smitten by a dragon catfishing as a pair of eyes in a book. She clearly has a type and Beast Boy definitely isn't that and no amount of shapeshifting would ever change her mind. Not to mention Beast Boy was in love with Terra until the very end.