The 12-year-old girl, who wasn't wearing a helmet, died in 2006 after 20 days in a coma.
Gov. Charlie Crist signed a safety bill into "Nicole's Law."
"Because of the hard work of Nicole's family and all her friends ... families in the western communities and all throughout Florida will be saved the pain and anguish the Hornsteins have experienced," said state Sen. Dave Aronberg, D-Greenacres, who co-sponsored the bill with state Rep. Joseph Abruzzo, D-Wellington. "Because of your efforts, children will be saved and families will be spared."
About 80 people attended the signing at The Acreage's Hamlin Equestrian Park, adjacent to an equestrian ring. The signing comes three years after Nicole's accident. Her father, Gary, traveled regularly to Tallahassee to push for the law.
As legislators pondered the bill, two other children were injured in horse-related accidents.
"This is truly a remarkable achievement because good legislation often doesn't happen for years in Tallahassee," Aronberg said. "It takes a groundswell ... The perseverance of all of you put it back on the agenda and when Gov. Crist came out in favor of it, it really rocketed that bill to the top."
Similar to the youth-helmet law for riding bicycles, Nicole's Law requires horseback riders 16 and younger to wear a helmet when riding on public roads and rights of way and while taking riding lessons. Rodeos, parades and private property are exempt.
Crist told the Hornstein family that while they cannot go back and change what happened, others can learn from those experiences to make children safe.
"This is about the future, about doing what's right, about making this a safe place to live," said Crist, a former horseback rider who said his sister was injured in a fall from a horse. "I know the courage it takes to take a family tragedy like this and turn it into something very positive for so many other people. My heart bleeds for you but also my heart sings for what you're doing for Florida."
Head injuries are the most common cause of death for people who ride horses or ponies, according to the American Medical Equestrian Association.
Under the new law, anyone who allows a child to ride a horse without a helmet would be fined $500.
Some Florida cities, including Davie, Plantation and Parkland, already have laws that require minors to wear helmets when riding, but the law makes helmets mandatory throughout the state.
"The ones that don't, they'll learn real fast because there's no margin for error," Gary Hornstein said. "[Nicole] did not have a second chance. It happened once and that was it. It was horrific and she went through things that no man, woman or child should ever go through."
C. Ron Allen can be reached at crallen@SunSentinel.com or 561-243-6611.