<Snipped quote by Rilla>
I think the point was that once she got out the arena, the guards wouldn't do anything to stop her because they don't know the child is an escaped slave. They're just walking around town doing their normal guard related activities so don't pay a lone child a second glance.
I don't know. A hole in the wall where fights are going on, is a pretty big giveaway. Unless the other guards in the arena are all "That slave is escaping... better not tell the rest" or "Let's not chase the girl through the hole."