Her body was found at the Moon Palace Hotel, where she was staying with her husband, TV producer Bruce Beresford-Redmond.
He is considered a suspect but has not been charged with the murder.
The victim's relatives say they need to pay for legal fees as they continue to seek justice for their loved one.
"We are pleading to the U.S.A. to help, because Monica, she's a U.S. citizen, and the family is grieving and mourning over just to think and know that her daughter is lying there dead and not bringing her home yet," said the victim's friend Mariza Alyrio.
Beresford-Redman's loved ones say they'll use the money they raise to keep up the pressure on the Mexican government to solve her murder.
Investigators have told Bruce Beresford-Redmond that he cannot leave Mexico.