provider of cake
You should really concentrate on one or the other. Too many attacking moves and not enough HP/Defense EVs means she can't take attacks as well as she should, but at the same time, running modest with a few special attack EVs won't be enough to significantly damage anything.
Sadly, the metagame hasn't been very kind to Cresselia, she's kind of setup fodder now for a ton of sweepers. Make sure you're using her to her full advantage.