Did she use puppy pads, newspaper, towels, or outside at the rescue. Whatever surface she went on there, make that available to her at home. If that was concrete and you have none, a hard, bare floor might work for her. Get her to go there then, wipe up but don't clean too well, leave a bit of the scent there. Place a pad or newspaper right beside where she went. get her using whatever you choose reliably then, work on going outside from there. Might take a couple of months to get there but, she will come around.