How To Litter Train A Feral Kitten?

I have a feral cat that has never been outside. She is about 8 months old, so she should be litter trained by now, but I’d like to start the process sooner rather than later. The problem with this house is that it’s very small and we live in an apartment complex, where there isn’t really enough room for her to use the bathroom without getting stepped on. I think she uses one of our beds as a bathroom (although sometimes she doesn’t know where or when to go). What do you recommend?