She was introduced by Abbie Youkilis, the aunt of 14-year-old Jaime Guttenberg, who was among 17 people killed in the February school shooting in Parkland, Florida. The girl's grandparents sat just in front of Giffords.
"We must stop gun violence," said Giffords, a Democrat who was severely wounded in a 2011 mass shooting in Tucson, Arizona, that killed six people. "Protect our children, our future. Let them lead the way ... make our country a safer place, a better place."
She told people if they "have the courage to fight, stand with me" and use their votes.
She and her husband, retired astronaut Mark Kelly, have campaigned for tightened gun restrictions.
Giffords and more than 100 other women gathered at a Cincinnati home for the launch of "Women for Aftab," backing Aftab Pureval's 1st House District challenge to veteran Republican Rep. Steve Chabot.
Pureval pledged to support equal pay for women and to protect health care coverage and paid family leave.
"You are the difference," he said, saying female voters can lift him past his opponent in November.
Chabot is seeking a 12th term in the traditionally Republican district. Democrats are hopeful about their nominee, who is coming off an upset victory in 2016 for the Hamilton County clerk of courts job.
House Speaker Paul Ryan joined Chabot in the Cincinnati area on May 31 to tout the GOP-passed federal tax overhaul. Ryan praised Chabot for promoting business growth.
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