Before Gwen Stacy died she and Norman Osborn had an affair, which led to Gwen becoming pregnant. She then gave birth to twins (Sarah, and her brother Gabriel) in France which were born early, but full-grown babies. After Gwen's death, Norman came to raise the twins and convince them that Peter Parker was their father and Spider-Man killed their mother. Which made the twins want revenge. They both were born with goblin powers in their system and aged quickly due to their healing factors.. Sarah looks like Gwen, and is highly intelligent.
After growing up, both twins wanted revenge on Spider-Man. After multiple fights, Peter convinced them that he was not their father. Gabriel figured out that their real father was the Green Goblin
and became the Grey Goblin
, embracing his heritage. Sarah objected and the three fought on the Brooklyn Bridge, where Stacy had died. Ironically, Sara was thrown off the bridge like her mother. She was saved by Spider-Man twice: the first was when she fell off the bridge and then after a blood transfusion to help mend a bullet wound.
Sarah went back to France and, according to the authorities, attempted suicide. What really happened was that she had growing pains because of her accelerated growing because of the Osborn gene in her. that's why she had to take pills to relieve the pain. When Spider-Man got there she explained that the pills were given to her because when she was younger she and her brother got along with the wrong crowd. She was keeping her brother in her house as well because he was also suffering. Mary Jane arrived just when Sarah confessed her love to Peter and kissed him. Mary Jane left in anger.
Spider-Man and Sarah were looking for the people who she messed around with when she was a child because they were trying to kill her. Sarah came back to to the mansion only to find that Gabriel thought that Mary Jane was her. Gabriel left with a glider and Sarah and Mary Jane reconciled and became friends. Before the Parker family left Spider-Man gave her a picture of her when she was a baby with her mother. Then Sarah started working for the government after Spider-man's good-byes.
Sarah, having the blood of her father, Norman, has superhuman powers like him. Sarah has super strength, which rivals the strength of Spider-Man. Also, Sarah's reflexes are much higher than a normal human. Sarah has good stamina, allowing her to exert herself to her peak for hours before tiring. Sarah can also heal from wounds at a faster rate than normal. A wound that would normally take days to heal would be healed in hours for her.