Sticky Situation

I recommended a friend of mine for a job that in the beginning I had little to no input on hiring, but after hearing that my boss who would have the most sway of authority (thumbs up or thumbs down) won't be there for her interview, I have to step in her place and have to look at hiring for the position in an unbiased way. The supervisor of the position, who is at the same level as my boss, doesn't like the idea that I know one of the candidates in the first place and I think, in turn, discredits her for the job before meeting her. I think she is biased already toward the other candidate based on that fact and also because the other candidate is a boy (that can do labor- a large part of the job). So I've tried to play down my friendship with this person to counteract the bad feelings stirring and have actually tried to explain to said friend/candidate what the situation is without giving too much away that could jeapardize her as a candidate. I'm trying to be professional throughout the whole thing, but now that I'm stepping into a bigger pair of shoes, actually being a part of the decision (be it not all, but enough), I'm feeling a bit awkward. I could push my friend's application for the job but it could be interpreted as me doing a favor for someone, or I could go for the other guy (if he is better, of course) and somewhat betray a friend without her knowing it. It wouldn't be that big of a deal if the said supervisor wouldn't have made such a swift judgement because I would feel that I wouldn't have to try to tip the scale back a bit to help balance the preconcieved notions. I can't "beef" up my friend anymore than I did a month ago but I can't ignore the other candidate either.
Next week the two interviews are scheduled. Wish me luck.