She is polite and understanding but immovable in the face of requests from a reporter and photographer in search of green onions. They want to get inside the Otay Mesa cargo facility, through which all trucks crossing the border from Mexico into San Diego pass.
The chain of command, up to Washington, D.C., and back, must be followed.
Once clearance comes, she's a gracious hostess in the cavernous cargo facility, with 105 docks filled with trucks carrying everything from television sets to pinatas to zucchini.
Hernandes is in charge of the customs inspectors at the facility. How many of them there are, she can't say. Security. She can't even say how many drug-sniffing dogs there are. But she can say how many trucks come through -- 3,000 a day -- and what the various inspectors do when the rigs are pulled over for scrutiny.
Customs officials work alongside inspectors from the U.S. Food and Drug Administration as well as local officials and U.S. Fish and Wildlife Service inspectors. The U.S. Department of Agriculture, formerly a separate entity with its own inspectors, is now part of her department, which is a division of Homeland Security.
"We're all one family now," she said.
Green onions are a pretty minor bump after the upheaval in her facility and other ports of entry around the nation after 9/11. Officials were more concerned with the heightened security alert issued last week than with possibly tainted produce.
Otay Mesa has not seen any shipments of green onions from the companies identified by the FDA as possible sources of the hepatitis A virus. Because the firms know that they can't get their onions across, they likely aren't shipping them.
Detaining trucks is not common, but it happens. The facility is big and busy.
"Sometimes it's bumper to bumper, especially in the afternoons," Hernandes said. Trucks line up to get into the portals, and then sometimes have to wait for a bay to open up.
Hernandes is assigned to keep the border secure, but at the same time, the philosophy is to work with shippers to try to get them across and preserve their loads.
If inspectors find a correctable problem, such as an infestation that can be killed by fumigation, they will turn the trucker around to correct it, she said.
Though the inspectors use lots of equipment, instinct and training are important, she said.
"The behavior analysis, yes," she said. "We see the drivers every day, we know the trucks, we know the produce. Every one of the [inspectors] has their own way of doing things, but watching behavior is important."