The organization announced Thursday that the Ruth M. Tankersley Trust awarded the gift.
Hanna Miller says the contribution was made in memory of her grandmother, Ruth M. "Bazy" Tankersley, and her aunt, Tiffany Tankersley.
Both women passed away within the last two years.
The family says both women were known for their love of animals and the Tucson community.
Ruth Tankersley founded St. George College Preparatory School and served as president of the Arizona Sonora Desert Museum.
The money will be used to help build a new welcome center for pets.
Maureen O'Nell, the organization's CEO, says the gift has inspired everyone and it will be an honor to pay tribute to both women.