My Ex Is Obsessed with a Teacher. HELP?

My highschool ex who broke up with me recently is extremely infatuated with one her teachers. The teacher is married with children already, but she seems to be madly obsessed with him. She steals his jackets and smells them, she flirts with him, she thinks about him all day and talks about him all day, she always wants to spend time with him, she gives him long and affectionate gf hugs, she treats him like how she used to treat me, and she broke up with me because the teacher didn't believe in highschool relationships. Now shes getting more and more obsessed with him its affecting her morally, societally, academically, psychologically, and her future. All her friends somehow promote her obsession with the teacher and so it gets worse and worse, and also the teacher seems to be leading it on as well. I still care for her and watch out for her, so what can I do to stop her from becoming beyond the point of no return?