I guess after being kidnapped so may times she finally learned to defend herself.

Snake: Mei Ling, tell me what you know about Peach.
Mei Ling: Princess Peach is the beloved ruler of the Mushroom Kingdom.
She's been kidnapped numerous times by Bowser.
Snake: Sounds pretty serious...
Mei Ling: Yes, but every time it happens, Mario ends up saving her.
Sure, he may not look like your ideal "knight in shining armor", a little on the short side, I'd say...
But still, don't you think it's romantic? I mean, to have a guy who's always there for you?
Snake: If he was smart, he'd tell her to stop getting kidnapped.
Mei Ling: ...you don't get a lot of dates, do you, Snake?