On Feb. 9, Maria, who has U.S. and Mexican citizenship, was kidnapped while outside of her home in the state of Colima.
"It's been 37 days," Zonia said. "At this point we need answers. We need to find my mother."
She said witnesses described seeing a white van drive onto her property.
"There was an exchange of words. She was refusing to get into the van. There was another individual who stepped out of the van and helped those two bring her inside and they drove away," Zonia described.
The mother of seven has not been seen since.
FBI offers $20K reward in case of missing 63-year-old American woman kidnapped from Mexico home
FBI offers $20K reward in case of missing 63-year-old American woman kidnapped from Mexico home
"We all started calling her to see if she would pick up her phone or answer her messenger and we have not heard from her," she said.
Zonia said investigators have ruled out that the cartels are involved but suspect the incident may be part of an organized kidnapping.
Lopez has lived previously in Southern California and still has family members in the region.
The FBI is offering a $20,000 reward for information leading to her safe return.
Zonia said they're confident Maria's fighting to come home.
"Us knowing how strong she is and that she's pulling, thinking of us seven and if we're bringing out that energy to her and we maintain those; we know we're going to have our mom."
The family has set up a GoFundMe page to help them in their search.
Anyone with information about Lopez's physical location should contact their local FBI office or the nearest American embassy or consulate.
In Los Angeles, the FBI can be reached at (310)477-6565. A tip may also be submitted online to the FBI here.
The FBI is conducting the investigation jointly with law enforcement authorities in Mexico.