She does require some finesse, not necessarily mechanical, but rather intelligence like someone else said, this makes her easier to master in theory, than someone like Riven with lots of mechanical finesse to play to it's fullest ability.
Irelia requires more than just mechanics to outplay your opponent. You have to know when you can go in, how long you can stay there, when to use your E for a stun, when to make do with the slow to snag a kill. And so on.
Irelia is the type of character who requires you to make evaluations, and be correct in them. Unlike someone like Riven who has lots of mobility, hard reliable CC and a short CD multipurpose defensive ability (which also works as an initiator).
Irelia needs you to make the correct decisions and if you made the wrong one you get punished hard for it, while this is true for a lot of others, truly mobile champions or champions with shields or other powerful defensive capabilities always have a way of protecting themselves from wrong decisions, and teh difficulty in playing them doesn't as much lie in knowing whether or not you can get out on top from the engagement, but whether or not you can mange it mechanically.
tl;dr: She's not mechanically intensive, but since her skillcap is lower she's got fewer situations she can dive into and do well in with pure skill. Therefore your decision to go in or not matters more.