Unfortunately, it's not strange to read about WW's hanging out with younger singles/divorced friends. As I described in my previous post, you will see uncharacteristic behavior in her. The more influence this friend has on her, the worse your W will probably behave. If you try to prevent the friendship, the more she rebells.
You can set boundaries for what goes on under your roof. If that woman is a potential teacher for your child, I think you have strong grounds to request another teacher (Should your child be assigned to her class). Take it to the school principal, and if that doesn't work, take it to the superintendent, and all the way to the school board. If they have another teacher of the same grade, then they should grant your request.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!