She's actually like, the one champion that
beats at all stages of the game.
Not saying she's balanced, but I think the biggest problem with her is the sheer amount of mobility she has, which makes her more annoying than anything else.
From what I see, Irelia is only really difficult to fight as a toplane carry. If you play a Tank or a Juggernaut, she's not all that tough to deal with, because your goal can't be to out dps her, her mobility makes it so she can avoid anything that's not a point and click. Your goal has to be to out farm and out last her.
So I don't think she's busted, I just think she's natually good against toplane damage dealers, because they all tend to rely on AoE, or some kind of aggressive mobility, which is easily countered by defensive dashing. From what I can tell, most tanks have very little problem with her at all, because they shrug off her early game damage, then buy armor, and can either ignore her entirely, or kill her with base damage if she gets cocky.