It is sort of unclear from your post exactly where the cat is inappropriately eliminating, but if you have had to change the litter material to compensate for recent surgery then I suspect that kitty isn't comfortable with the change. I realize that you probably cannot make use of normal clay litter at this time for post-operative care reasons, but since you have a kitty that is choosing her place to comfortably eliminate, perhaps you can place pee-pads, newspaper or other material down where she is going in consideration of her condition until she can again utilize her regular litter material.
You can also use dry uncooked beans- it feels like litter, they like to dig in it and it won't harm them or get into sutures- same goes with rabbit pellets (rabbit food) and the alfalfa in the pellets stop the smell of urine from going to far. If the kitten has been declawed, that is why she is not using the litter pan. Her feet are sore and tender and she does not feel like hopping over the side of the pan to land on them. I would put down puppy pads for now, or put the rabbit pellets on a cookie sheet so there are no sides for her to deal with.
She may also find bit uncomfortable (as in it hurts her) to pee and she is associating that with the litter box and hence she thinks going elsewhere to do her thing. You may have to be patient with her until she feels better and use regular litter again. And use lots of newspaper and pee pads - and lots of deorderizer - until she is feels back to par again.
Thank you very much for your input. She still goes next to the litter pan. As to using deoderizer I'm afraid. Because whenever her brother smells smth on the floor he starts sneezing. So we have a couple more days that the vet recomended not using the litter for and then hopefully once we go back to the litter she'll know what to do.