I mean, to be honest, it's just me being more annoyed that I can't reach her, than that there is something wrong with her. But I still think it's stupid how little she can actually do.
It just seems that she's "hard to play" because of the lack of abilities, rather than the difficulty of using them. Then again, difficulty with such things are complicated... According to Riot, Cassiopeia has a 100 difficulty rating, but to be honest, I think certain other champions WAY more difficult to play. All it seems you do as Cassiopeia, is poison people and spam Twin Fangs.