She's never gotten constant nerfs. She was adjusted a lot after release, like most champions, then her AP build effectively got removed.
After that her W sustain was lowered a long, long time after.
After that her base stats were buffed.
Long after that her E's base damage was hit.
Long after that her Q damage was buffed.
Long after that her ult CD was hit.
And now her passive was changed.
Outside of that, there were minor base stat adjustments (both buffs and nerfs). We're talking entire **seasons **, somtimes more, between hits outside of the ult and passive changes.
Almost every nerf/buff was a direct result of a change to Trinity Force/BotRK, not Irelia randomly resurfacing in the meta without any provocation.