Tracey was on a mission. She was infuriated by Daphene's actions and her flippancy at the whole 'getting disowned' situation. Tracey would have given anything to be from a family like the Greengrass's. Sure, Tracey's family before her were a prominent pureblood family, but then her dad went and fucked it all up for her, then became a complete embarrassment. Tracey had spent the better part of her life trying to cover up his mistakes. And Daphene had thrown everything away after it was practically handed to her on a silver platter.
But even worse than Daphene's situation, was how much she hated the Weasleys. So when Tracey had gotten an owl from Daphene's sister with a plea for help, Tracey couldn't say no. After all, Tracey loves helping people.
She arrived at Daphene's door and knocked loudly. The thought of the altercation that was about to happen was enough to put a smile on her face, albeit a small one. Her face muscles were going to ache later from actually being used for once.