Irelia

she didnt, you got dementia/alzheimer's from playing riven -

Irelia's stun occurs off %. Meaning if your % is higher than hers (Doesn't matter if she has 3000 max hp to your 2000) she'll stun you.

There's no way she stunned you if she had higher health %. You must've miscalculated things.

Irelia vs Riven is one of the most tense top lane match ups, the one that gets the first blood of the match up will win the game. Probably you weren't paying attention, and you used your stun on her first and then she beats you.