The adventure-loving girl from Newport even missed her mom Kate's 50th birthday and brother John's 18th in the past year.
Speaking on the anniversary of her disappearance, Mrs. Omerod said, "I'm terribly worried about Kirsty — and we fear something awful could have happened to her.
"She is a bit of a free spirit and has done her own thing in the past without telling us.
"But she has always contacted us after two or three months.
"It's a year now since she went missing, but what is worrying more than anything is that she did not get in touch on my 50th birthday in May and John's 18th in June.
"It was so unlike her not to contact us on these two big birthdays."
Kirsty, who will be 21 next month, flew to Chicago from her home in Maindee, Newport, to see her favorite group at the All State Arena on November 16, 2002.
Records show she booked into a hotel in the city and left four days later.
That is the last known record of her whereabouts.
The band made a public appeal for help from other fans to trace Kirsty.
A band spokesman said, "Wherever you are Kirsty, please get in touch with someone to let them know you are safe. Please come home soon. Everyone is really concerned."
Her description has been circulated to ports and airports on both sides of the Atlantic, but there has been no firm sighting of Kirsty.
Interpol has also been brought into the hunt, as Gwent Police, who are co-ordinating the search, become more and more concerned for her safety.
Detective Sergeant Mark Warrender has contacted police in Chicago, who are making fresh appeals and circulating her description throughout the USA.
He said, "Kirsty was expected to only be away for a few days.
"We are making fresh appeals for information from anyone who has heard from her or knows her whereabouts.
"Concern is growing as time passes, because she has not contacted members of her family or friends to say she is safe and well.
"We are still keeping an open mind and hope she will pop up one day.
"She has been known to do her own thing at times but never outside this country," he added.
"It is possible she is still in the USA. We thought at first she may have been following GUNS N' ROSES to other concerts across the States, but their tour ended long ago.
"We know she used her cashpoint card to withdraw money in downtown Chicago when she checked out of her hotel, but there has been nothing since."
Mrs. Omerod said, "We are just praying that she is alive and well and has made friends in America she is staying with.
"Another important date is December 6, when she will be 21, and we hope she might contact us then."