This wouldn't be OK with me either. She will be distracted from either you or driving, and neither is OK. If she is in private practice I expect the only thing you could really do is tell her that you don't want to do this and why. If she is at an agency, I would consider talking to her supervisor and seeing if that is policy. Either way, unless I was seriously attached or felt she was particularly good in other areas, I would consider terminating. It just seems like really bad judgement which would make me not trust her.