Tsubaki doesn't really have any reason to like Ragna when you stop and think about it. I mean when she was apart of the NOL, he technically was a criminal and still is. And everything that's happened between her, Jin, and Noel has him at the center of it all(Jin abandoned the NOL to go after Ragna, and Noel then went after Jin), and now she's aware that he's a disaster waiting to happen. That, and she's obviously jelly of the yaoi him and Jin got going on.
I find it funny how much hate Ragna has gotten from this girl despite not doing anything to her directly, it's like everyone hates Ragna for one reason or another. It's gonna be quite interesting to see her reaction to Jin being his brother, and Noel technically being their sister, I look forward to that.