She raised £4,400 in memory of Nick Beaumont, her ex-partner who died from a cancerous brain tumour in January 2020.
Kier, aged 45, works for Rotherham Doncaster and South Humber NHS Foundation Trust (RDaSH) as a community psychiatric nurse in the Child and Adolescent Mental Health Service.
Kier said: “Nick was only 56, he died so quickly after his diagnosis.
“I needed something to help me get through the pain of it all, so nine days later I signed up for Ultra White Collar Boxing, which organises events for charity.
“The tournament was originally scheduled for March last year, but the Covid-19 lockdown delayed it until this year.
“It wasn’t easy but I felt really proud when I won.
“I did this for Nick and my boys and if the money I raised prevents just one family from going through what we have been through, it will have been worthwhile.
“A massive thank you to everyone who has supported me.”
Cheering ringside at the racecourse were Kier’s family and friends including step son Will and sad John Ellis.
Her son Maxton who is aged seven said “she is the best fighter in the world.”
Kier has worked for the NHS for 25 years and is currently based at Tickhill Road Hospital.
Her fundraising page is open for donations - click here.