NFL commissioner Roger Goodell released a statement later Sunday.
"Mrs. Mara was a tower of strength, dignity and inspiration for her family and all of us in the NFL," Goodell said. "Her family and the Giants organization have always reflected Mrs. Mara's competitive spirit, integrity, and wonderful sense of humor. Our thoughts and prayers are with John Mara and the entire Mara family."
The Giants were founded in 1925 by Tim Mara, who was Wellington's father. Wellington's nephew, also named Tim Mara, sold the other 50 percent of the team to the Tisch family in 1991.
Ann and Wellington Mara were married in 1954 and had four sons, seven daughters, 43 grandchildren and 16 great-grandchildren. Two of the 43 grandchildren are well-known actresses -- Rooney Mara and Kate Mara.
Of the 11 children, three work in the Giants' front office -- John as president and CEO, Chris as senior vice president of player evaluation and Frank as the vice president of community relations.