I could not find a way to describe it with few words, the only vertices available nearby are at the bevel. The line desired would be straight with the y axis (hopefully that provides more options)
Edit: I thought I just found the solution, but it did not work. I tried moving one of the vertices on the 90 degree line all the way down to the end of the red line and turned on snap to edge. The line made does not seem to make more faces, when I select some of the perpendicular faces it goes right through the haphazard edge I made. I also tried selecting these two vertices again and hit F to fill.