Garcia-Bratcher was arrested the next day after an investigation. She's expected to make a first court appearance Thursday on a single felony count of inflicting injury on a child.
Lt. Steve Brown said Monday it is not clear what prompted the assault.
The boy told deputies he didn't know why the woman grabbed him, Brown said. There appeared to be no connection between the boy and Garcia-Bratcher's daughter, such as a shared classroom or lunch area, he said.
"We can't prove these kids had any interaction," Brown said. "Did she get the wrong child? I don't know."
Brown said it was possible the boy was lying. But he said statements from witnesses coupled with photos of the red marks "leads us to believe it happened."
But Garcia-Bratcher insisted Monday she didn't touch the boy, who her daughter said called her a "dirty Indian." She said another student told her the boy grabbed his own neck right after the incident, saying he was going to get Garcia-Bratcher in trouble.
"This is crazy," said Garcia-Bratcher, a mother of six kids, who was free on $30,000 bail. "I'm on the news. I feel like a monster."
Her lawyer, Ben Adams of Santa Rosa, vowed to take the case to trial.
"If the state files charges on this all offers will be rejected," Adams said. "Let's see what a jury thinks."
Meanwhile, Superintendent Jennie Snyder said school officials handed out fliers Monday morning to parents explaining what happened and reminding them to check in with the office before visiting campus.
Garcia-Bratcher apparently didn't do that before coming on campus Friday afternoon to enroll a younger child in kindergarten. The school requires all visitors to sign in and get a visitor's badge.
Snyder said there's a policy against bullying on the K-6 campus of 320 students but she didn't elaborate. Jennifer Burton, who has three kids at the school, said administrators have been lax about pursuing bullying complaints. She said she reported another student saying inappropriate things to her daughter on Facebook but nothing was ever done.
"This is not the first incident," Burton said. "I understand where this mother is coming from."
While she sympathizes with Garcia-Bratcher, Burton disagrees with the way she's alleged to have handled her daughter's situation.
"I have been in her shoes," Burton said. "But I didn't go to the extreme she did."