teaching a stray adult cat to use the litter box

i just “adopted” a rough stray cat from the streets. she’s been to the vet twice so far but will not use the litterbox. she does not have any veterinary issues that would cause this aversion. i’ve tried everything, treats, different litter types, mixing soil in since she lived outside, placing her inside of it, nothing works. if i put her inside the box she freaks out and doesn’t want to stand in it, regardless of the litter type. everyone says cats have a natural instinct to want to bury their feces and dig, and mine will scratch on the carpet and try and “bury” her business, but will not go in the litter at all. what do i do?