You might consider a substrate that will keep them worn, than a clipping intervention.
Dog toe nail clipper can work, but with box turtles it is difficult, because, well they can box themselves up. If you do it, you can use a cork from a wine bottle to keep the shell open, and cut the smallest amount, a few times over several weeks. Keep something like this on hand if you go to far . https://www.walmart.com/ip/Blood-St...447Fr5_gdkvzr5DwsuqIOQr7YJPGemzxoC7qYQAvD_BwE
Substrate solution is easier. Garden soil. Add worms, she will dig to get them. Back nails may need a trim no matter.