Why?
If anything, I'm impressed by Ozma's tactical mind and reasoning. She's got good logic and she's cautious, yet she knows that the Fables need to deal with the threat quickly before it escalates. She's both active and passive depending on the situation, and yet she clearly isn't going to rush into things blindly based on how she proposes recon and analyzing the magical spells.
I think Frau may have good reasons to give Ozma a chance.