I don't know your set-up, but I have an indoors cage with fleece. For the toilet I've bought some plastic rabbit corners which are easy to take out and clean. you can use newspaper and hay or megazorb or anything absorbent to fill them. I usually put a layer of hay on top and more in one corner.
If you have a hutch, just put an extra wad of newspaper where she decides to have her toilet spots. You will find that many piggies are quite tidy and are peeing only in certain spots. Many also have their pooing places, though never exclusively.