Someone fishing for early retirement.
Fire her, hire someone young + qualified.
Probably just the opposite. She probably wants to keep working, and they're forcing her out to hire someone younger and cheaper. It's very hard to fire a teacher who hasn't done anything wrong, so they just make the older teachers miserable 'til they leave.
I have seen this happening in my school district near D.C.: they transfer the older, more experienced, and thus more expensive teachers to unspeakable areas, and sometimes subject them to harassment or even to dangerous conditions until they get sick of it and quit. Then they hire a 22-year-old who can barely read and write and certainly doesn't know how to handle a class.