I am promoting Bonnie to Fox Highlander, and she "fainted" in the fight of the sewers. I know that the companion you're promoting must accompany you in every fight for their promotion, and she was revived for the fight with frog fishermen. However, she had 1 wound. If she's to perform her best, she should not have any wounds at all. Maybe you can change this. (Although it probably won't because this is the way the system works.)

Perilous Zoe Nightingale, level 59
P.S. I know a companion gets 1/2/3 wound(s) if you manually revive them