Try to punch her between the legs

The blonde is covering her belly so you need to find another target.

Mandy is leaning back against the corner and her legs are slightly spread. There might be just enough opening between the BBW's massive thighs to hit her crotch.

This idea is not something you are proud of, but given the unfair size difference, it should be okay to try somewhat questionable tactics.

You kneel down pulling your fist back and swing an angry uppercut to the blonde's bulging camel toe.

"OOAHH!" Mandy moans as your hard knuckles suddenly smash her fat pussy.

You feel a satisfying jiggle as the soft mound is flattened between your fist and the blonde's pubic bone. For a moment the BBW stands still with her mouth wide open before she slowly collapses down on her huge ass massaging her cunt.