"Hey girl," she said, laying flowers on the earth.
In reality, Villalvazo never met the child long known only as "the little girl in the red socks."
But she was determined not to let her be just another anonymous statistic in the wave of violence against women and girls in Mexico.
Lupita's semi-naked body, beaten and sexually assaulted, was found in a Mexico City suburb on March 18.
No one came forward to claim her, and for months, she was known only by the clothing she had on when locals found her in a vacant lot: a pair of bright red socks.
Villalvazo, a 47-year-old journalist and women's rights activist, first read about the case in the local newspapers she monitors every day in an attempt to document Mexico's epidemic of violence against women.
The problem, which has lingered for years, exploded into the headlines again in 2017, when 7.5 women were murdered per day, according to statistics from the United Nations and the government -- a new high after three years of decline.
Villalvazo, who goes by the pseudonym "Frida Guerrera" (Frida the Warrior), did not want the girl's case to end as just another unsolved homicide in a country where 99 percent of violent crimes are never punished.
She asked authorities for a picture that could help identify the girl. But she never received an answer.
"The authorities' silence is a touchy subject. The message they send is, 'We don't care. We're not going to do anything,'" Villalvazo told AFP.
"In Mexico, it's no big deal -- you can kill a woman, a girl, rape her, torture her, kidnap her, and absolutely nothing will happen to you, because they don't investigate. Because it doesn't concern them."
Finally, a confidential source passed Villalvazo a bloody crime scene photo, which she was able to use to create a composite sketch of the girl.
It was the first step toward identifying her and finding her killers -- a long journey that took a decisive turn Wednesday when prosecutors finally announced the girl's identity at a press conference, shortly after arresting her mother and stepfather and charging them with her murder.
Searching for Lupita
Villalvazo published the sketch of Lupita everywhere she could.
That ultimately led two of the girl's aunts to get in touch with her last November.
In interviews with AFP, they described the girl's short life as one of abuse and abandonment.
"She didn't deserve this," said one aunt, Marina Concepcion Medina, 39.
Lupita's parents never registered her for a birth certificate, and she was bounced around from home to home -- at one point living with garbage pickers.
Marina and her sister Luz Maria Medina, 33, asked to take her in after noticing bruises on her and other signs of abuse.
"I told (my sister), 'Leave her here.' Lupita grabbed my hand and told me she didn't want to leave with her mom," Luz Maria said.
But her mother refused.
'They did nothing'
Mexico has a law setting out harsher sentences for "femicide," or the killing of a woman when gender plays a part in the crime.
It was passed in 2007, amid an explosion of women's murders -- notably in Ciudad Juarez, on the US border, where hundreds of women were raped, killed and dumped in the desert or simply disappeared without a trace.
Despite the law, violence against women rages on with near-total impunity.
"The state has been incapable of reversing the years-long trend of high rates of violence against women. These cases have not been adequately investigated," admitted Pablo Navarrete, legal coordinator for the government-run National Women's Institute.
Lupita's aunts had scathing criticism of the official investigation.
"They did nothing," said Marina.
"Not the prosecutors. Not city hall. The authorities are useless."
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)