SACRAMENTO — The California Senate was forced from its chamber and halted work for more than three hours on the final day of its session after an opponent of mandatory childhood vaccinations poured what appeared to be blood on lawmakers from the gallery Friday evening.

Stunned lawmakers left the chamber and security officers cleared the gallery and floor after the 5:14 p.m. incident.

The California Highway Patrol said it arrested a woman who “threw a feminine hygiene device containing what appeared to be blood onto the Senate floor.” The agency said the liquid landed on several senators.

“That’s for the dead babies,” the woman shouted as she threw the liquid from the balcony overlooking the Senate floor.

A video posted on Periscope showed a woman dressed all in black, repeatedly saying dead babies’ “blood is on your hands” as she was surrounded in a Capitol hallway by CHP officers. She was eventually handcuffed and led away.

The CHP identified her as Rebecca Dalelio, 43. According to online property records, she lives in Boulder Creek outside Santa Cruz. She was booked on suspicion of six crimes, including assault and vandalism, and was being held on $10,000 bail.

Dalelio has regularly shared posts on her Facebook page that support consipracy theories about vaccines.

In the Senate chamber, red splatters could be seen on the desks of several lawmakers.

State Sen. Steve Glazer, D-Orinda, tweeted a picture of a menstrual cup containing a red liquid. He said in an interview that he was one of the lawmakers splashed by the substance.

“The nurse took it from my head,” Glazer said of the liquid. “They’re suggesting I take a shower, so I’m going to go do that.”

Sens. Cathleen Galgiani and Melissa Hurtado appeared to be among the lawmakers hit by the liquid. Galgiani, D-Stockton, was visibly shaken as she left the Senate floor.

Hurtado, D-Sanger (Fresno County), tweeted, “I took an oath to give the Valley a voice, that includes fighting for policies that represent the diversity of my region which has been neglected. No one said the fight would be easy. Today’s event was an unacceptable example of the challenges we face. As always, we’ll rise above.”

The incident happened on the Legislature’s last scheduled day of business for its annual session. Senators returned to their business around 8:30 p.m. after taking the extraordinary measure of relocating to a large committee room. Legislative staffers carried in computer monitors, printers and paper stacks of their agendas.

“A crime was committed today, but the Senate will not be deterred from conducting the people’s business,” said Senate President Pro Tem Toni Atkins, D-San Diego.

Opponents of mandatory childhood vaccinations have besieged the Capitol for days. Within the past week, the Legislature gave final approval to bills giving the state more power to review medical exemptions for children from vaccinations for such diseases as measles, mumps and rubella that they must receive to go to school.

Gov. Gavin Newsom signed the measures, but vaccine opponents have not given up their protests, insisting that the vaccines pose health risks to young children. Medical experts say the risks are remote and are far outweighed by the danger that lowered levels of vaccination among schoolchildren and society at large will lead to a resurgence of diseases that have been controlled or eradicated.

Sen. Richard Pan, D-Sacramento, who sponsored the vaccine legislation, was shoved from behind on a Sacramento street in August by a vaccine opponent who videotaped the incident. The man was cited for misdemeanor battery.

“As their rhetoric escalates, their incidents of violence does as well,” Pan said in a statement Friday night. “This is an attack on the democratic process and it must be met with strong condemnation by everyone.”

Shock rippled through the Assembly as lawmakers heard about what had happened in the Senate. Some expressed concern that the protesters could target them next with a similar display.

Majority Leader Ian Calderon, D-Whittier (Los Angeles County), said the Assembly added extra CHP officers and security staff to the gallery in anticipation of protesters on Friday. He said members had lost their patience after multiple interruptions from anti-vaccine activists as the Legislature tried to finish its business in the final week of session.

“We understand that people may disagree with what we do, but this kind of behavior is just unacceptable,” he said. “It’s just a lot of frustration and disgust with how (protesters) seem to be handling themselves.”

At a candlelight vigil outside the Capitol, where they carried small symbolic caskets and displayed photos of children they said had been injured by vaccines, protesters said they did not know the woman who had been arrested.

Ian Wilkerson, a 40-year-old father of two from the Bay Area, said it was unfair that her actions were distracting from his group’s message.

“It is a mischaracterization of our movement,” he said. “I would never sanction such disgusting opposition.”

Denise Aguilar, an anti-vaccine activist who helped organize protests every day for the past two weeks, said parents were still crowding into the Capitol to send lawmakers a message that they’ll react in force to any future bills cracking down further on vaccine exemptions.

“We want them to know we are now watching,” she said.

Dustin Gardiner and Alexei Koseff are San Francisco Chronicle staff writers. Email: dustin.gardiner@sfchronicle.com, alexei.koseff@sfchronicle.com. Twitter: @dustingardiner @akoseff