Having lived in SF under her reign as mayor, I don't have a lot of regard for her, but given how rich hubby is, I don't think you could bribe her with anything less than drilling rights in a big oil patch.
I think this was a move purely to avoid energizing the GOP base. It was possibly made in consultation with the Clintons. It also could have been that she was in fact chosen by the Dims in the Senate as the committee member who could most afford this vote.