From her own account, she sounds like she was being a sanctimonious cuntbag. If I was unloading a cart while my partner ran herd on a couple small kids and some snooty twat came up and was all, "You should help her" and "This is America, you have equal rights here and you're allowed to ask for help" I would tell her to fuck off, too. Physical assault and pressing charges is over the top, but I can certainly understand the impulse to trip her condescending ass.
If she'd actually wanted to be helpful, she would have OFFERED TO HELP. Directly to the woman. As in, "Can I help you unload?"