I don't think fixer fit the bill here. Maybe I'm influenced by Cyberpunk but fixer sounds like someone with indirect influences. Cleaner fits better in this case.
In "Sakamoto Days," the term "Cleaners" eventually becomes "Floaters" (those responsible for cleaning up the area after a serious incident).
From what I understand of the context, "Fixer," as translated by Kay, refers to a group responsible for investigating and "eliminating" anyone who might interfere with the balance of the "underworld." It's "fixing"/"arranging," not "cleaning."
Since (apparently) she's not connected to the "normal" (civilian) world, using the term "law enforcement agent" wouldn't be appropriate, after all, she's illegal.
PS: Have a good rest, Kay, and thank you.