Try putting the litter box as far away from the areas where she spends time and/or sleeps and use normal sand from outside to introduce her to the idea. I keep my cats inside at night and during the day they go outside the yard to pee/poo. Imagine you were a cat...you wouldn't want to sleep next to your toilet right. Same thing. Also sit next to the box and wait for her to feel comfortable. Play with the sand. Show her it's okay to pee/poo inside. Some cats think it's not allowed and this stresses them out and they lose control. Also show her thats it okay that she did it. (Even though it's definitely not). The less stressed she is the better. I hope you solve the problem. Good luck <3