The 39-year-old mum of two says she is still suffering from obesity and struggles to lose weight because of her spinal condition, anxiety, ADHD and post-traumatic stress disorder.
Speaking to Daily Mail, Knapp Wilkinson, from Missouri, said she only found out about the photo after her sister found it and asked if it was her.
She then scrolled through hundreds of cruel comments that poked fun at her obesity.
"The worst thing about this photo is that people think a fat woman tipped over a cart because she was too lazy to get out of the cart to get the case of soda," Knapp Wilkinson wrote in a candid post on Quora.
"I have a condition in my spine called Spondylolisthesis. The most common symptoms in the legs include a feeling of vague weakness associated with prolonged standing or walking.
"In my case, the longer I stand the more numb and weak my legs become. I have been known to fall because of this condition."
Knapp Wilkinson was grocery shopping for her husband Robert when she fell off her scooter and was in enormous pain
"My parents had a form of this disease and had to have back surgeries in their early 30s. So there is a good chance my children can get the same spine disease," she said.
She shamed bullies for assuming her obesity was because of "laziness", saying the photo was now an eternal reminder of a "low point" in her life.
She said, "I was at a very low point in my mental health. I also was experiencing a lot of pain and weakness that day. I took a cart because I was grocery shopping for my family. I went to get a case of soda for my husband.
"I thought I saw a flash of light and heard some young girls giggling. I thought nothing of it because I am use to hearing people make fun of me or saying snide remarks. It was nothing new.
"I have also seen this photo attached to stories that aren't even true about this situation," she went on.
The stay-at-home mum said she wanted people to know "fat people are people too" and wants "compassion, understanding, and respect as a fellow human being".
"You cannot see my disabilities but they are there and they are real. So next time you see photos making fun of people just remember you know nothing about these people or the struggles they face every day," she added.
"It is never just harmless fun to laugh at someone."