Hired? Not really. They tried to convince her to help, but she claimed she wouldn't. She could be after the bounty in order to get her party raised. We know from the dryad that the bounty is dead or alive, but that he is worth more alive.
However, as she said, plans aren't her strong suit. I find it hard to believe that she would come up with the idea of pretending to be his ally so that she could take him in alive. As far as I can tell her plan is to rescue him while wearing a disguise she didn't even believe would work so that he doesn't recognize her.