[@Asuras]
As a little kid, she basically followed someone else's orders in order to kill some fatty. Just given a gun, given a location, and various edgy shit happened before she point-blanked the dude. Dude that was supposed to pay her just cut off all connection with her instead, so she made do with whatever was in dead man's pockets.

After she recovered from the initial trauma (or maybe she never did), her mind began to equate killing people with money, so her first major purchase after 'food' was bullets for an empty gun. Shop owner (or street peddler?) would have thought she was just some low-level grunt working as a runner for some low-level gang, so probably overcharged her a ton. But she made the bullets pay for themselves and then some.

Was really just mugging with murderous intent until she worked out that she can double-dip. Steal dead people's shit AND get paid for capping them.

Essentially, it was something she got tossed into and never came out of. I just assumed that in the future, firearms are so easy to handle that even kids can use them.