>>716510250
She's been drawn in different ways over the years depending on the artist. Mostly giving her human feet makes it easier to draw her bare legs without having to come up with creative ways to "connect" the webbed duck feet to the rest of the body without giving her absurdly thin and long legs.
Besides, it's not the first time a Disney bird has been drawn with normal feet, Gyro for example always had human feet even in the original comics.