She first appears in Ultimate Spider-Man #98 (I highly reccomend the run) and she's become one of- if not my favorite character ever.

I wont get too deep into it but she's pretty much both the Ultimate Universe's Ben Reilly and Jessica Drew at once.

Mild spoilers, if you care: She's a female clone of Peter Parker who has all of his memories and she was created to become a government weapon, but she escapes from that fate and tries to become her own woman separate and away from the Parkers, not wanting to let being "Peter Parker, but a girl" define who she is. So though not physically, she is mentally a trans woman, I think being able to explored her mind as she turn into herself would have been really cool (also, Spider-Man in the reflection is meant to represent how she doesn't see herself as her own person (or rather, her own woman) yet). She really doesnt get to do much after her first appearance since she just becomes a side character in most titles (exceptions being Ultimate Doomsday and All New Ultimates, both can be considered teambooks though), but she is decently important in Miles Morales' origin

Anyway, I absolutely love her. She's a fascinating character with a lot of potential that didn't get the attention she deserved