Fostering sick stray cat

Hello. It’s my first foster and I’m very happy that I am able to help this sick teen cat. Took her to the vet and is on meds for 2 weeks. I keep her in a cage for now cause she needs to be isolated from my other cats. She has possible upper respiratory infection and she must not have direct contact with other cats.

We are on Day 6 of medication. She eats plenty and her nasal discharge has lessened. She pees and poops normally, however, whenever she uses her litter box to pee/poop she does not bury it. She lays on the cat litter with the pee/poop. I read that it has something to do with it being a familiar scent. But do you have any other tips on how I can prevent this? I don’t really want her sleeping on her waste.

Thank you!