90% Tenacity (which has no effect against knockups, suppressions, or knockbacks) was only 'reached' by having 3 champions near her, the Tenacious mastery, a tenacity item, an Elixir of Iron, and use of the cleanse summoner spell. It isn't really a common number to reach since Irelia prefers 21/9/0 masteries in most matchups, benefits from the Elixir of Wrath (more damage agaisnt squishy champions, nice increase to sustain), and pretty much never takes the Cleanse summoner spell.
Irelia is a good champion against squishy champions, so she excels against ranged top laners. However, Irelia has a weak early game in which her main goal is to survive, so picking a strong early bully can crush her. However, keep in mind that her base damages will still kill squishy champions, so I'd recommend building pretty tanky against her.
Irelia is not a tank; she doesn't really have the CC or defensive steroids to classify her as a tank. In actual play, her function is closer to an assassin/fighter. Irelia will typically build Trinity Force, then get tanky enough to survive diving into the middle of the enemy team to kill the enemy team's squishy champions or a drawn out duel with a bruiser/tank. She may or may not get a second offensive item at some point (Typically Blade of the Ruined King, Ravenous Hydra, or Zephyr).
As for Irelia getting a double kill when ganked by the enemy jungler, that's honestly pretty common top lane on most champions. It typically happens when the top laner is winning their lane and denying their opponent, so their opposing laner is so far behind they can't really contribute to the fight. Ganking a Rumble or Riven player improperly when they have ultimate can easily result in a double kill for them, as another example.
When playing Irelia, I found that the champions I had the most trouble with were:
Darius has a very strong early game and typically builds durable, so he can easily bully Irelia off CS. His Crippling Strike reduces attack speed and movement speed, which hinders Irelia's ability to trade. His damage is very bursty, however he can still beat Irelia in an extended trade. I'd recommend starting Cloth5 or Doran's Shield and building Brutalizer into Sunfire Cape on Darius to abuse your base damages and survive trading with Irelia.
Nasus and Mundo outscale Irelia, are capable of handling her in the early game, and have comparable sustain. Mundo's cleavers can be used to kite her when she tried to trade, Irelia doesn't have enough burst damage to reliably kill Mundo through his healing, and his W reduces the duration of Irelia's stun. As Mundo, I would recommend starting Cloth5 or Doran's Shield and building Sunfire Cape. Nasus has the sustain to survive the lane, Irelia is weak early so she can't bully him too hard, and his Wither can cripple his damage output. As Nasus, I would recommend starting Cloth5 or Doran's Shield, getting an early Giant's Belt, and building Frozen Heart.
Malphite can cripple Irelia's attack speed in fights, has a shield to survive trades in lane, and is too tanky for Irelia to kill. Malphite also provides strong initiation, so your team can focus Irelia while you occupy their team.
Riven is mainly a skill matchup with Irelia. Riven's third Q and her W can be used to interrupt Irelia's autoattack animation to prevent damage during trades, Riven has a stronger all-in, and her shield can absorb damage when trading. While you have to play well, you can force trades well in your favour and bully Irelia away from CS.
Swain is a ranged champion, however he can become quite durable with a Rod of Ages and his natural sustain. Swain should probably max Q first in this lane as it is a reapplying slow (so Irelia's passive doesn't affect its duration) and Irelia has to stay beside you to trade. Swain should be able to bully Irelia with his ranged abilities and autoattacks early in the game and become durable enough to fight her after level 6 with his ultimate.
