Maybe you could wet a piece of toilet paper with her pee and put it on the litter box. She will smell the pee on the litter box and pee on it.

It worked out perfect with my cats: they always peed on the litter box.

However, when they want to communicate something, usually not good, they would pee out of the litter box. Once one peed on top of my dining table!

Maybe she is trying to tell you something!

Ah, I always caressed them and said how nice they were peeing on the box. Until, finally it was a good habit. My little big rugs were safe!