The little five-year-old, who won the hearts of people here and around the world, lost his battle with cancer last week.
Danielle Johnston, a personal trainer at her husband Will's Sculpture gym on Balmoral Road in Belfast, was on the receiving end of a torrent of abuse after she was accused of using Oscar's name for self-promotion.
In a post on Monday evening, Danielle wrote: "I think it's really sad when poor wee Oscar had no choice with his illness and tried to fight it as much as he could.
"When people know the dangers of being overweight and unhealthy but continue to do so.
"Changing your lifestyle isn't easy but it's definitely worth the blood, sweat and tears for a happy healthy life."
Just hours after making the comment Danielle was forced to remove her Facebook account because of the volume of abuse directed at her.
However, comments continued to gather on the gym's Facebook page, with one user posting: "Horrible vile people. Trying to gain interest in your gym off the back of the tragic death of young fearless Oscar is the lowest of the low. I hope this destroys your business."
The fitness expert said she was devastated at the result of her post.
"It's just been a complete nightmare. I didn't even think when I put up the post, and it wasn't written in the context that people have taken it," she said.
"The post was up for a while and people were actually liking it, but then one person commented negatively and the abuse just kept coming.
"I put an apology on straight away, to make it clear I meant no offence in relation to Oscar, but it had moved on from that – it was personal attacks on me and Will.
"I had death threats and people from America messaging me to tell me they hated me.
"Last year at Sculpture we ran a campaign to raise money for Oscar and we have sold wristbands for the great cause the family continues to campaign for."
An emotional Danielle, who was set to fly out on her honeymoon last night, told the Belfast Telegraph that she regretted the post and was being kept going by the messages of support from people who know her. On Sunday thousands of mourners attended the funeral of wee Oscar at St Bernard's Church in Glengormley before hundreds of lanterns lit up the city's night sky as people moved by his fighting spirit paid tribute to the five-year-old's legacy.