I think it depends upon the process. If a vacancy has been advertised and she has applied, in the same way that anyone else could apply, there is no interest to declare, but for the sake of transparency, I suggest that you mention that you encouraged her to apply. You can still participate in the discussion and vote. On the other hand, if there was no open process to fill the vacancy, you have given her favourable treatment and it would be unwise for you to participate in the discussion and vote.
As you have mentioned, if everybody who discussed a vacancy with a friend or neighbour was ineligible to participate in the selection process, quoracy might become an issue.