Maybe there is something to the brand or type of cat litter that she does not like? If it is scented litter, try using unscented. The chemical fragrances they use in cat litter can cause allergies in cats, oftentimes showing up as ear infections.

The fact that she is going to the bathroom at the doorway of the litterbox shows that she knows it is where she is supposed to go, but she doesn't like going into it. Is it a covered box with a lid on it? Or is it just a pan? If it is scented cat litter with a lid covering it, the chemical fragrance will be more overwhelming than if it is just a pan without a cover.

Try using the brand "Scoop Away, Super Clump, Unscented." It doesn't have those chemical fragrances in it.