She has pretty low damage that still requires you to aim, her ult is worse than useless without some team coordination, she has the largest headshot hitbox in the game, she has almost no mobility when trying to put out damage, her primary form of mobility to get in to effective range knocks people out of her effective range, and she only counters Winston.
And Winston does everything she does except more consistently, and frequently better, so why even bother picking her except for winky face spam.