It's always easiest and probably best to take the high road in those types of situations, either leave or remove your dog to another section and keep it away from hers. There's no real way to "win" the argument and in the mentality of promoting peace for all people at the park try and stay away from fights. If the person was kicking your dog in a corner and not stopping of course stand up right away for the dog, but for little spats like that it's really not worth the breath or aggravation.
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 5 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010