Mayday Parker was a New York vigilante who rose up to fight criminals as Spider-Girl. She is the deuteragonist Spider-Man 2099.
Mayday Parker was a daughter that Peter and Mary Jane Parker born at some point during the 2020s. She inherited her father's abilities and became the vigilante Spider-Girl, at some point developing a Spider-Cave.
In her 50s, Mayday started being plagued by heart problems from the effects of fighting crime. She started using a hi-tech Spider-Suit developed by Stark Industries that augmented her physical abilities and allowed her to continue the never-ending battle for a while longer but injuries suffered through the long decades of physical punishment and an ailing heart finally took their toll, and even the suit couldn't compensate any longer.
In 2079, after her heart started acting up during an attempt to rescue a kidnapped heiress she was forced to go break her personal rule of never killing anyone just to defend himself after suffering a heart attack in the midst of the fight.
Mayday decided to hang up the mantle of the Spider-Girl for good, living a life of solitude with her dog Peter.
In 2099, Miguel O'Hara figured out that Mayday Parker was Spider-Girl. Wanting revenge on Tyler Stone for killing his father, George O'Hara, Miguel stole Mayday's advanced Spider-Suit and went after him as he was about to strike a deal with a foreign weapons dealer about a shipment of chemical weapons.
At first Mayday used a remote command to lock down the suit, but after Miguel convinced her, she begrudgingly agreed to help him. After Miguel managed to stop the deal, Mayday, impressed with his performance, offered Miguel a chance to take up the mantle of Spider-Man under her guidance, to which Miguel agreed.
Mayday would view as a mentor and informant of the Spider-Man of 2099.