Her death is tragic. I am somewhat surprised that as a teacher getting a flu shot was not mandatory unless there was a doctor’s excuse.
She probably did get one. The article doesn't say one way or the other. In fact since the article says the school went to the trouble of doing some sort of "deep clean", it seems likely that the school would have made flu shots mandatory for their teachers.
Whoever wrote the article probably didn't want to point out how ineffective "store-bought" medical treatment really is. They just wanted to play on the expense angle as if that is what caused her death.