Don't know how you're getting 850 rape cases. It said she had called one victim over 850 times.
I believe there were 2-4 students. One married her. The article is quite vague on the ages, although I think a teacher should never get involved with a student even if they are of legal age.
Edit: Re-reading, that's what she was charged with, "pleaded guilty to two counts of improper relationship between an educator and a student." Not rape, so they were of legal age.