The British makeup artist, who suffers from Crohn's disease, thought her two-piece days were behind her after she was fitted with two colostomy bags in 2010, but on a Christmas vacation in Mexico, her husband, Ian, persuaded her to strip down.
"My husband always said to me, 'If we go on holiday, I want you to wear a bikini. You've got a great body,' " Townsend, 23, told BBC Midlands Today.
"The first day I was like, 'Okay, let's do it.' I'm not gonna see these people again, that's how I looked at it."
Townsend, who's battled the intestinal disease since she was 3, had given up modeling after she had the bags fitted when her bowel burst and she nearly died. "My confidence was totally knocked," she says.
Sofia Bouzidi / Cater News
"I felt like I finally had the confidence after three-and-a-half years of having them that I wanted to give other girls the confidence, the guys the confidence, to be like, we have nothing to be ashamed of," she says.
She was surprised when the photo went viral, being viewed by millions, and says the response has been so positive that she's now planning to return to modeling part-time.
"I never thought it would get a response like that," Townsend admits. "For me it's just a picture, but to so many other people, it's so much more."