Certainly, it is wrong to blur the lines between the priesthood and the laity, but if it clearly a role that is acceptably held by a lay person, why exclude women?
I think there are probably hundreds of qualified men available to fill the needs of the children at the OP’s high school. THEY CHOSE TO PLACE A WOMAN IN THE SPOT. To me that says it all.
Why does it matter if there are hundreds of qualified men? Why should they give preference to a man in this situation? Are women only fit to be parish secretaries and members of the altar society? In my all-girls Catholic High School in the 1980s, the position was called Campus Minister. For the first two years, we had a female Campus Minister. For the 2nd half of High School, the Campus Minister was male. The job consisted of planning school Masses, encouraging student involvement in spiritual matters, planning retreats, running the campus ministry club, planning student service opportunities etc. (I’m sure there was more to the job, but from a kid’s perspective, that was about it.) We had a priest, our chaplain, who was available for those occasions that required a priest - school Masses, Confession, etc. There was considerably more student involvement in campus ministry for the two years that we had the male- he was young and good-looking, so all the high school girls flocked to campus ministry. Not exactly pure motives, but it got us involved. Attendance at the early morning (optional) Masses skyrocketed.