As long as she doesn't get a critical hit or outspeed you, you should
win by using Power-Up Punch twice, although keep in mind that even if
you lose, nothing bad happens, you don't lose any money, and you'll
still proceed through the storyline.
After the fight, Korrina will suggest that you take the Lucario with
you on your journey.
In other words, if you lose, you still get the Lucario and by extension, the Lucarionite