>>16739916When I've played on Showdown, after the first hit, she loses Parental Bond.
If you're not running an Adamant Smogonmum, unless you get a crit, it takes three hits with Crunch to kill a 0 HP EV, 252 Def +Def or even a Neutral Def natured Cofagrigus.
So assuming you switch on the Power-Up Punch and M-Kanga goes for the Crunch, it wouldn't hit the second time and you have two guaranteed more turns, assuming she stays in.