How do you itemize against a fed Irelia?
If you're a tank or fighter, one of the armor items that reduces attack speed will do an ok job at dealing with the bulk of her damage, hitting the physical and auto-attack portions. Omen, Heart, Warden's Mail all work reasonably well against the likes of Irelia or Jax, and they come with an added benefit they aid the squishier members of your team even if Irelia doesn't focus you.
If you're a marksman or mage, Guardian Angel is the best defensive item you can get against most anti-carries. They dive you, slap the taste out of your mouth with their combo, then there's this awkward pause where they didn't get a kill or resets, and are sitting in the middle of your team. It's incredibly hard to effectively wipe out a priority target with GA, and even with dying twice - you usually cause significant problems.
In both cases counter-building a fed champion requires your team sticks together to help one-another deal with the Irelia. If you let a fed champion roam the map forcing 1v1s, they're only going to get more fed.
Generally speaking fighters and assassins are better than average duelists and worse than average team-fighters as well. That's pretty much the case with most snowbally champions.
Irelia isn't to extreme in either direction, but from what I've seen - she does excel more in 1v1 situations than team-fight situations, so grouping up (preferably not in single file) will negate a bit of Irelia's power.
into her build before the late game. If that happens you're well and truly boned.
