She'll likely pull fur shortly before giving birth. You should give her the nesting box a couple-three days before she's due. If you want and you have access, you can just cut or pull an armload of tallish grass, let it dry in the sun, and give her that. You can also use straw, but unless you have other animals who need bedding, that's not the most convenient thing to store. She'll hopefully start gathering up the dry grass you give her shortly before she's ready to deliver, but if she doesn't, you can put it into the nest box for her.
Sometimes they mess up and deliver on the wire or they don't pull fur, or maybe they don't make the nest. Just do what you gotta do. She'll prolly figure it out. Mine seem to deliver at night, so you might want to keep an eye out, in case she has any problems getting things sorted.
