The Newstalk presenter launched the 'Memories are Made of This' dementia show garden in Dublin's Phoenix Park, dressed head-to-toe in 1950s attire.
Dr Kelly was at the event with her son Blaise (9) and his best friend Lily Bateman-Cullen (9).
"I'm delighted to be involved," Dr Kelly said, as she explained her role as ambassador for the garden - part of the HSE's 'Dementia: Understand Together' campaign.
Dr Kelly's mother Julie (91) died in 2017 after suffering from dementia.
Tragically, Julie couldn't remember who her daughter was and struggled to recall her own grandson.
The broadcaster told how her mother called her the "girl with the kind eyes".
"I do think dementia is stigmatised, and the HSE have done studies about this and found over half of people wouldn't like to know or be around someone with dementia," she said.
"Age is the biggest risk factor, so a load of us will get dementia and if we don't, a family member will.
"I think we need to move far away from stigmatising it and actually start to deal with it."
Dr Kelly said there was a "lot of joy and fun up to the end" between Julie and her grandchildren, despite her illness.
"It's hard for them losing someone they love," she said.
"But I think they had a lot of joy from her and felt a connection with her, even though she had dementia.
"I try to focus on the happy memories - I don't think you can do anything else - and I like being involved in this, it's really positive."
The garden features gnomes, pink flamingos, haycocks and tea roses, a fruit and vegetables patch and a High Nelly bicycle, all memorabilia from the 1950s.
The garden was created by award-winning horticultural designer Robert Moore, a double gold medallist at Bloom last year.
David Bateman (62) and his wife Mary (61), who has dementia, visited the garden, along with Tim O'Looney (80) and his wife Rita (78), who also has the illness.
"I remain positive and do what I can," Ms O'Looney, from Templeogue, Dublin, said. "It's not easy at times as I forget some words but, in general, I do my best."
The couples attend the Alzheimer Society of Ireland's Bloomfield Social Club in Rathfarnham, south Dublin, and encouraged others to try to attend similar events.
Dr Suzanne Timmons, clinical lead for the HSE's National Dementia Office, said recreating memories through a garden or in the home was key to helping someone with dementia.
She added that triggering memories can "empower" those with dementia, as they struggled to remember the everyday but can often recall their past with ease.
Meanwhile, 'Derry Girls' actress Nicola Coughlan was at Bloom to open the 'Yesterday, What If' show garden, which is sponsored by Universal Pictures Ireland.
She revealed she and the rest of the cast had met the "real Derry Girls", the friends of the show's writer, Lisa McGee.
"Lisa writes the characters with such love - they're gas women, they're brilliant," she added.
Bloom starts today and is on from 9am to 6pm every day through to Monday.