Sorry, I should have cited examples:
Vasyl Lomachenko (male) at 130-135 has the skill and the experience to knock out a huge lumbering dude. Yes, huge lumbering dude poses a threat but less so if he's not on that elite level.
We can assume that Cara Dune is elite.
In 2008 Carano weighed in at around 144 pounds. I'm sure that at that weight her *character* can put some yokel tough guy to sleep, and in real life? The possibility is absolutely there.
Don't believe me? Find someone trained, talented and experienced who's smaller than you and let them hit ya right on the button.
So basically this 140 pound will only run into big men who have no idea how to fight. Got it.
That guy you mentioned just give up his belt to duck a fight with a 20 year old kid.