Hit her back.

You use an opening she foolishly left for you and kick up as hard as you can. You can feel as your feet connects with a soft flesh of Emily's pussy. She gasps, but you are hitting her again, this time in her lower belly with your heel, not giving her the time to recover. The air is knocked out of her, but you can guess that she's suffering a terrible pain in her lady parts.

Your girlfriend always complained about how painful it was on her period, so you had a bright guess that actually kicking in that area would cause much suffering to the victim and, judging by Emily's curled up on her knees and sobbing, you were right.

You stood up, still holding your crotch. A dull ache continued to throb in your nutsack, so you felt no pity for your attacker's plight.