Melanie Soap was Amy's assistant in her store, Bric-A-Brac, for a long time. She is the daughter of Judge Soap, a magistrate of a very imposing stature and a severe hatred towards smugglers. Melanie was an art-school classmate of Amy's, and later ran a magazine called Fact'r (along with a guy named Chloron) which lost money on every issue. Amy was able to get her to leave this and work at her newly-founded store, on the grounds that this was a job which actually paid money, even if it didn't make so much use of her design skills. However, after a number of years working for Amy, she quit this job in order to join the artisanal hamburger craze as a waitress for Bank of Burgers. Her interests include vintage medical equipment.
Ryan saved Melanie from the fire in Amy's original store (set by an enraged mob who had been misinformed by the thrift-shop ladies that it was a brothel, in order to remove the other shop's competition). This resulted in Melanie being attracted to Ryan and beginning a relationship, though this ultimately soured when Melanie's father was injured in an incident connected with a smuggling scheme that Ryan was involved in (where her father was acting as a vigilante trying to stop the smugglers), after which Melanie began shooting at the bad guys.
In the alternate timeline of "The Case of the Forked Road", Amy works alongside Melanie at the restaurant, and there's some possible romantic involvement between Melanie and Ryan in a time when in the main timeline Ryan is already married to Amy.