Yeah, I would talk about this for sure. Also, I agree with others who have questioned this friend.

A friend respects your wishes. Are you even sure she was being truthful when she said she got your appointment?

I see nothing irrational about your upset here, or any reason to minimize your feelings. In fact, you have every right to ask that your friend stop seeing this therapist. If it bothers you, then, in any friendship, this should at least be open for discussion.

I had friends like this in therapy and it took both my therapist and me to put their brakes on their behaviour.