I think my master slave cylinder or maybe CSC just went

And FYI, if you have the tools (probably not at your GFs place) and the confidence that with time you could do it (seems you do), I would think just about anyone who can follow instructions can push the pedal. If it's likely they've never done anything like this before, you definitely want to demonstrate on another car's brake pedal. I had my wife practice first on her Acura (with it on to make it easier) to get a feel for the speed, and explained that pumping too fast would cause air bubbles and set us back further and take more time. That got her attention since I already told her that her leg would be sore after we were done

Oh and I use ATE Super Blue and ATE 200 (gold) and switch between them when I change brake and/or clutch fluids. It makes it easy to tell when you've cleaned out the old fluid It can't handle the heat quite as well as Motul, but it's better than stock and does just fine for braking during "spirited driving".