The story of Lourdes Lizardi, in the video player above, is part of the new CBSN Originals documentary, "Border Business: Inside Immigration." Watch the full documentary at the bottom of this page.

When waves of so-called caravans, convoys of migrants mostly from Honduras, arrive by the thousands Tijuana, Mexico, activists like Lourdes Lizardi are increasingly struggling to find them safe and secure shelter.

For 24 years, Lizardi has been working in shelters across Tijuana, Mexico's busiest crossing point on the U.S. border. Recently, her job has gotten much harder. Flimsy tents crowd the streets of the Benito Juarez Sports Complex, an outdoor facility and one of about a dozen such makeshift shelters across the city. Children try to entertain themselves with whatever they can find. A toddler pushes an empty stroller along the concrete. Another young boy ran up to Lizardi inquiring about a toy car he found. He wanted to know if he could keep it. "Show me the little car and I'll give it to you," Lizardi said.

Over the past year, several organized caravans have made their way to Mexico. One brought 7,400 more people to an area where space was already severely limited and resources sorely strained. Activists like Lizardi were overwhelmed.

"Where should we put these people, our migrant brothers?" she said.

Lourdes Lizardi helps guide migrants to a makeshift shelter in Tijuana, Mexico. CBS News

Many of the migrants here are waiting for their turn to turn themselves in to U.S. authorities in the hopes of being granted asylum. In spite of the challenges, Lizardi says she's determined to keep people safe while they wait.

Lizardi sometimes has to relocate beleaguered families and individuals as Tijuana officials declare certain areas prohibited and open up new ones nearby. She paces up and down the streets with a megaphone, warning migrants what could happen if they don't move to the new shelter she and her colleagues recently opened.

"I've only come to let you know that this is the final call," she announced. "Whoever stays here will do so under their own responsibility. Starting tomorrow, the government is coming to clear the street. There is another shelter up there for everyone."

"No one is prepared, even less so in Tijuana," Lizardi said. At the busiest border city, security is a constant concern. "There are groups that take advantage of all this movement," she said.

But she feels strongly that all the migrants, wherever they're from and whatever brought them here, deserve dignity. As she leads a group to their new shelter, Lizardi says, "You are not numbers to us. ... You are our brothers. You are our sisters. I just want to tell you that."