IMO there is always a chance that someone is bluffing. BB could be trying to steal the pot on the turn /w a raise on a drawy board.

Since the CO is unkown, I think he could easily have an overpair here (how many times have you seen donks stack of with overpairs in situations like this at micros? I've seen it quite a bit)

You have a SET, and are only losing to 68, 63 (unlikely given PFR) A3, and a higher set.

If the BB really has the range you say she does, then I'm not quite sure what to make of her bet. Like someone else said, I'd like to see you put some ranges into pokerstove and calculate our equity.