Tracey was furious after her conversation with Marcus - no surprise there - and didn't dare go home. If she bumped into Patrick, he'd be able to guess what was wrong with her in seconds. She also didn't want to go and see her ex-husband- It was his fault Marcus was even in their lives.
Instead Tracey changed into Muggle clothes and Apparated to an alleyway near where Callahan lived, walking quickly to his front door and knocking. She did hope he was in- Right now she needed somebody who didn't know Marcus and who wouldn't stick up for him. She needed somebody who would just comfort her anyway.
"Hi," she said, smiling back at him and feeling her anger subside a bit. "Thanks- Sorry to just stop by but... I can't go home. I'm absolutely furious and- It's too difficult to explain right now but I just want to hide from life for a while. Can I?"