Several things were confused Kaylee right at that moment. One, this seemed to be the person they were looking for, but Rhia hadn't seen her. Granted, she assumed that because Rhia had said the Doctor, and that's how this woman just introduced herself, but two - who introduced themselves as 'the' Doctor? Then again, three, didn't Rhia say he?
She suddenly realised that she'd been asked a question, and was being offered a hand. Smiling, she shook it. "Oh, no, sorry, she's not, we're just..um...we just met, and we're looking for..." she trailed off. Considering it for a moment, she decided that this woman couldn't possibly be who they were looking for, so Rhia must just refer to her Doctor friend as 'the doctor' - like Mal did with Simon. "Who are we looking for, Rhia?" she asked "Doctor who?"