I-Am-A-Silver-Lining
Summary: Corvin wakes up. She's a cat now. A big, fluffy cat with no idea how it happened or why. She thought things were crazy with just that, but then she meets a familiar face under a different name and things get even crazier.
OR!
In which a modern-girl falls into the Marvel Universe and is shifted into a cat. Bumps into Tony Stark and decided to follow him home because he's a magnet for trouble and she had a bleeding heart and a low-key-hero-worship-hard-on for Iron Man.
Some mythological/magical bullshit happens later, but Marvel was already full of that before she got there, totally not her fault.