I'd give her some time to acclimate to her new home. Natasha came to live with me in August, and she peed on the couch constantly until about November or December. She continued to pee on my lap when I was at the computer for another month or so. Since January, though, she hasn't gone outside her litter boxes at all.
Until that happened, I kept a towel on the sofa, over a puppy-training pad, and watched her carefully. When it looked like she was backing up into a corner I'd say, "time to use your litter" and shoo her into her cage. That helped a bit, as she learned she could go into her cage and use the litter without being locked in right away.
Mostly, I think it was a territory-marking thing. Once Natasha settled in and accepted that she was home, everything was fine. Oddly, I could tell she'd crossed that boundary the day she started paying attention to the stuffed bunnies.