This story is a prequel to The Amazing Sunset Shimmer
https://www.fimfiction.net/story/467263/the-amazing-sunset-shimmer

Because she sealed a pact with Mephisto Pheles, a famous stuntgirl becomes, by night, the armed arm of the prince of evil whose disastrous hegemony is coveted by his own son.

Death-dodger by day, biker vigilante after the sunset,
Spitfire will have to fight to save the ones she cares about.

This story takes place in the EGFU: Equestria Girls Fiction Universe

And there came a day unlike any other, when two remarkable people met.
Both have done things they regret.
Both framed for crimes they didn't commit.
Both forced to run from people they thought they could trust.
Starting over for a second time, a girl from another world takes up a new name and a familiar tool as she finds the world she's being calling home for the last three years is not as simple as many thought.
It's a world of The Mighty.
A world of The Fantastic.
A world of The Uncanny.
A world of The Amazing.
A world.....of Marvels.

Copyright goes to Hasbro and Marvel Comics.

Vinyl Scratch is a carefree girl, she passes her classes, mixes on the weekend and generally lives a pretty relaxed life. However after a trip to Crystal Corp and being biten by a radioactive spider, she must now learn that with her great power comes with great responsobility as Canterlot City's new protector. Vinyl's going to have to learn how to balance her normal life with her life as Spider-Woman, fighting for something more than herself for the first time.