I think like with lots of medical issues the handling of mono has changed over the years - when I was growing up a long time ago, someone with mono was basically put on bed rest for two months or longer as much because of the possibility of them being infectious to others as for their health. A lot of people have only minimal symptoms, and a bunch of others only have acute symptoms for a very short period of time. Some people it lays out for a long time, but that is not very typical.
Heather was diagnosed during training before her freshman year and had missed all of the preseason and the November games. Having not played in any games there was a decision to be made at the end of Nov or maybe early Dec. - she could easily have returned to the team, but if she played in a single game she would not have been eligible for a medical redshirt. She had missed a lot of training and being a freshman didn't have team experience to fall back on so she would have been way behind the rest of the team. She, her parents and the coaches decided to take a 'redshirt' year rather than lose a year of eligibility when she would have been so far behind. She did however practice with the team for most of the rest of the year and Geno as I recalled praised her for pushing Tina hard in practice - so much praise that most of us were expecting more from her the next year than she ultimately was able to deliver.