Her tone was very different in her streams. She's a very awkward, boring, paranoid woman. In her streams, she'd often look around like people were watching. But, she was perfectly acceptable in playing the games, being pleasant enough and not saying much.
With Phil, when they first started she was egging on chat and being a smarmy trolling bitch, much like Phil. Phil has a way with making his women adopt his shit behaviors. Which she never was in her streams. That changed quickly when the chat gave it back to her, and she could only keep her eyes glued on the chat in horror.
It's hard to say if Catherine was depressed, but she obviously has mental issues. That vacuous stare, says little, seems paranoid.