Fred wasn't paying attention to the conversation between the flying boy and the knight-king-mayor candidate. She was trying to get people out of the way, and they weren't exactly moving like she wanted. Everyone wanted to watch what Fred was only somewhat aware of. Oh, she was aware enough to be able to help Jack out if something were to happen, or even to help the boy if he got hurt. Yet, she had to get the people out of the way.
"Move! Now!" If she'd had a gun, she would have pulled it out and shot it because that usually worked in the movies. Though they never quite explained how something or someone didn't get injured by the bullet - going up or coming down. That did bother her on occasion. probably part of the reason she wouldn't do that little trick.
Some people noticed that the "frail" brainy type really could look a little tougher. She knew how to protect herself, and she could actually put the hurt on someone if she had to. She just preferred not doing that in most cases. They were indeed starting to move.