we set up rules when he started facebook and the first one was that he can't add anyone that I don't approve of him adding, also that everyone needs to be someone he personally knows and has had face to face contact with. I also told her these rules and she seemed to think they don't apply to her.
I haven't asked him what he thought, however I do think he added her because he wanted to please his dad. I will ask him if he cared that I removed her.
I think it's a slight over reaction on your part. Like it or not she is going to be part of his life as long as she is dating his dad.
And Redlesley is correct with all of her points below.. :D
The first question that comes to mind is - what does your son think about removing her seeing as he's the one that confirmed her as a friend? Did you explain to him why you removed her and the reason?
I would guess that he may feel resentful about what you've done if you've given him permission to use it in the first place.
By allowing him access to facebook you have now opened up a huge area that needs boundaries and agreements.