You can isolate her in your bathroom. But I've had 3 different cats that responded differently each time to litterbox training. My first cat, Rusti, hated the texture of litter initially. So I went outside and filled a small box with dirt. She used it, and I slowly started mixing litter in with the dirt. My second cat, Angel, was pretty difficult at first. She would only go on towels, and seemed to refuse to go anywhere else. As a last ditch effort, I took some soiled litter from Rusti (who was the only cat free of parasites and whatnot) and put it in Angel's separated litterbox. She started using after that.
My present kitten, Marco, has been the easiest. I stimulated him to go on a soft tissue, and buried it in some shallow litter. He does have accidents, but that's because he's in a carrier or a playpen and they both are too small for a even the smallest box. So I have to take him out when he cries at me and place him in his box, now that he's old enough to go on his own. He sometimes hops out but putting him back in several times until he goes works. Since your kitty has already gone once, I don't think she'll have much issue going again now, especially if you isolate her in the bathroom with her box and place her in there when you think she needs to go a few times. Always keep a little bit of her soiled litter in there after doing a litter change, too. Kittens are even more scent-reliant than adult cats are, so if there's no scent of her own waste, she could likely forget that's where she needs to go. You don't need to do this too long, I had to do it for 2 litterbox changes for Marco. But it could take a bit longer for her.