Switching between domains

We have a consultant who joins our LAN (NT domain)whenever she’s in the office. When she leaves, she would remove her WInXP pc from our LAN to join her company’s. Each time she returns our administrator has to re-join her pc since an admin password is required. Is there a way to allow her to automatically switch between 2 domains without involving our administrator? We’ll probably continue this trend due to security reason but I’m interested to know we have an alternative.

Thanks for all help.