Not....webbed feet.

Webbed feet is when there is ... webbing, skin connecting between your toes, like a swimming flipper, as a duck does, though its usually not that pronounced when it occurs in humans.

Hers have been deformed by her wearing extremely poorly fitting shoes her whole life, and/or possibly just had fucked up toe alignment to some extent, to begin with.

More like foot bondage, but less extreme, and self imposed.

Think of how if your teeth grow in funny, you may need braces to better align them.

Well, this is sorta like that, but where the shoes are functionally the braces, and they're all fucked up and force the toes into an extreme configuration over time.

EDIT:

Basically, MTG is Cinderella's evil half or step sisters.

They kept jamming their feet into badly sized and badly formed fancy shoes, and at least in the original version, they actually cut off parts of their feet to try and literally fill Cinderella's shoes, but the Prince kept noticing the blood, and them walking awkwardly.

MTG has just been jamming her feet into, eh, likely needle point pumps of some kind, for so long, that they've smushed her pinky toes under and behind the adjacent toe, and the other toes have splayed out to compensate for the lack of balance that causes.