Advice on TNR release and litterbox issues

Ok so I have now done my second true TNR. Last time I did this I ended up going from 3 indoor cats to 7. She is currently in my utility room healing after surgery Friday. My concern is she won't use the litterbox. The first night I left her in the trap for a couple hours while the anesthesia wore off and she did go the bathroom then. I was cleaning the cage today in between doing laundry and found she peed on a small pet bed I put in the kennel with her. I still have yet to see a second bowel movement though.

The humane society where I had her fixed suggests using crystals, pine, or paper but she won't use any of it. She has never used a litterbox before but this is the first time I have had a cat not use the litterbox. Even 4 of my cats were feral kittens when I caught them and they took to the litterbox immediately.

She is in a large dog kennel so there aren't many places she could go instead or so I thought. I have tried mixing all the litters and even using a layer of dirt on top with no success. I would rather keep her inside for a few more days to make sure everything is ok but I don't know if I can if she won't use the box.

Any suggestions?

Just a note, she was a feral kitten but between the TNRs I care for and daily feedings she is extremely friendly to me. My original hope was to work with her till I could see if the Humane Society could evaluate to see if they would be willing to take her to adopt her out.

i have found that cats unfamiliar with the litterbox will go on fabric type stuff if it's on the floor, so you may want to remove the pet bed until she learns. if there is absolutely no other place in the crate for her to go other than the litterbox, i think it will kick in quickly. i'd also just fill it with pure dirt to begin with, that will be the most similar to what she's used to. sprinkle some catnip on it, this may attract her.

the recommendations from the humane society are really for housecats, but when you're dealing with ferals just worry more about getting her to use any litter for now. good luck!

Oh I've had this problem before. 2 things I did - one I got a cover to a large trash bin, (shallow and mostly flat) put it upside down and filled with pine pellets and some sterilized dirt. They used it right away!

2nd thing I tried for a different feral was Pee Pads for housebreaking
doggies, with a small mound of pine pellets. They caught on really
fast and when they used it consistently, I put the pee pad and
pine pellets into the shallow trash bin top, then after they used
that for a bit, got a larger deeper box. Et voila, they had learned
to use the box!!