don't guard them with your face. Obviously not right after one of them has been elbowed in the nose.
And if one of mine accidentally elbows a defender in the face and she was not excessively swinging her elbows, I tell her, "She shouldn't have been guarding you with her face."
But as I mentioned in the first elbow swinging thread- all my defender has to do is change her arm position to cross her arms at the wrist, stick her open hands up in the players face to obstruct vision, and now the elbows can't contact my players face without first hitting forearms or wrists.