I just let her bite me. Maybe not the smartest way to go about it but it didn't hurt and she eventually stopped. I did not put her down or back in her cage until she calmed down, I don't know what they are capable of 'learning' or not but didn't want to show her that biting worked.
I've never heard of tapping them on the head, but there is more that I don't know than do so...
Besides, Peggy Sue was an all knowing, all seeing eye when I went near her cage and if I had tried to tap her head it would have only equated to putting my finger in her mouth and making it all that much easier for her