My own child did the exact same thing as yours. I hate to say it but I finally bit her back. I tried everything you're trying and nothing worked. People kept telling me to bite her back so she could see what it felt like. I didn't want to because to me it felt like I was abusing my child. One day I just had enough and gave her a little bite on her arm after she drew blood on another kid. She kind of looked at me like WTF, shed a few tears and hasn't bitten since.