Melanie Walker was first introduced in the animated series Batman Beyond as a member of the Royal Flush Gang, a group of costumed criminals who had been stealing for a considerable time and all of whom were members of the same family.
She served as a love interest for Terry in the same way that Catwoman did for Batman (Bruce himself even alluded to this) She was a character that was inclined by pressures to be both good and bad.
As the youngest member of the group she had the most in common with Terry McGinnis (the current Batman). Melanie entered Terry's life when he was having relationship issues with his girlfriend Dana. The two began seeing one another but Melanie could not bring Terry to meet her family because to do so would mean that Terry was willing to become part of the family. Terry discovered that the Walker's were really the Royal Flush Gang and during a fight Melanie was forced to side with her family against Batman (not knowing he was Terry). Terry (as Batman) was forced to had her over to the authorities.
Melanie was later released (as she was a minor) but received word that her family had been kidnapped by the Jokers. She began committing crimes to free them and once again crossed paths with Batman (who did not turn her in this time). She briefly hid out at Terry's home (Terry allowed this as he was torn between his feelings for her and doing the right thing) but left so as not to bring any more trouble down on him. Melanie soon discovered her family's abduction was false, and it was really a test of her loyalty to her family (which wavered when she met Terry). When the Gotham Mob and police soon arrived on the scene looking for the Royal Flush Gang, Melanie abandoned her family.
Terry, as Batman, payed a visit to Melanie who was now working as a waitress to make ends meet. She had nothing to do with her family (which had fallen on hard times) and after they were all once again arrested even bailed out her older brother Jack (who she cared for).