An employee of rival fantasy sports company DrafKings reportedly won $US350,000 by using insider information when playing a game on FanDuel's site.
The controversy has caused outrage across the US and could hurt a growing business.
With Sacco quoted in statements defending the company, critics have been quick to take aim at her for landing a job in the loosely regulated industry.
One Twitter user by the name of @edzitron said: "I love that Justine Sacco is the PR person to defend the daily fantasy sports gambling world. It's perfect, I could not love it more."
Another suggested maybe it's time for Ms Sacco to get out of the PR game.
Ms Sacco told the New York Post the issues facing the company have nothing to do with her personal history or events she has "previously acknowledged and apologised for".
Ms Sacco sent her infamous tweet back in 2013 to 170 followers as she boarded a plane for South Africa. The tweet went viral while she was mid-flight and she landed to her own PR disaster.
In an interview with Jon Ronson in The New York Times Magazine earlier this year, Ms Sacco tried to explain her AIDS tweet, saying there was no way she thought anyone could have thought it was anything other than an ironic joke.
"Unfortunately, I am not a character on South Park or a comedian, so I had no business commenting on the epidemic in such a politically incorrect manner on a public platform.
"To put it simply, I wasn't trying to raise awareness of AIDS or piss off the world or ruin my life. Living in America puts us in a bit of a bubble when it comes to what is going on in the third world. I was making fun of that bubble."
