Smart move. She got used to the super speed and having that cut off mid-fight must've been disorienting. She's still an experienced (if a bit captive/sheltered) knight though, and she has that swiftness amulet to boot, so I'm not sure who will win. I hope she wins though, because it'd give cause for the MC and FMC to move on for a new arc while likely obtaining the approval of her father which'd hopefully include the ability to leave.
The muscle mommy can just ignore the bet and follow the MC anyway, unless she ends up being a stickler for such a rule, but then that'd be a waste of a potentially interesting character whom we could get her perspective on growing up and dealing with her senses growing slower with her training and why she'd continue to train despite that.
