Hmmm, there must be a rough patch of wood in the hutch somewhere that Roxy is catching her foot on. Have a thorough check in there. Also check any other places she might have been for sharp or rough places. For now though, she definitely needs vet attention, infection can be nasty for any animal, as it's more than likely it will become an abcess, and if an abcess gets really bad it can KILL. Bathing in salt water sounds like quite a good idea, but it would be hard to hold her in a bucket of salt water as it'll probably sting a little and she'll want out. You could try dabbing it with a sponge or something soaked in salt water. Please keep us posted on how she is, if you can.