I thoroughly checked the tank and all parts to it. Nothing was cracked or leaking light that I could see. If it was the tank, I suspect the second roll would have been fogged much more than it was given how extreme the fogging was on the other roll. A crack or hole in the tank would need to be fairly large and obvious to get the extent of fog present.
But, it does seem that the tank and light baffle has to be the culprit. To get that "V" the film would need to have been folded over itself if something fogged it from the outer edge or the light would have to radiate out from the center if the film was wrapped around something. Looking at the pattern, the fogging is worse between the diagonal lines of the V-shape. The angle of the diagonal lines seems fairly consistent so the film was probably being held in some sort of symmetrical orientation when it was lightstruck.
Maybe the flange was mistakenly placed up in the tank to cause some sort of gap on one side. The "V" might be spokes in the reel blocking fog coming from one edge although I would imagine any lines from that would be curved due to the spiral holding the film. I did ask the student if she had any trouble locking the tank which usually is the case when the flange is upside down. She again said she didn't have a problem.