Don't know about the steps but I think there are many things you can do with your kids to teach them about body language.
Play a game of 'Faces' and make a face and have them guess how you are feeling. Do this out in public as well (discretely or people may become weirded out).
Ask your child to tell you how they are feeling about a certain thing - does this make you happy/sad/etc. Why do you feel this way?
You can also do this game without using faces but instead hands/arms/legs.
Use specific instances "You took the ball from me and look over and see me looking like this" mad face or frowning, arms crossed. Ask "How do you think I am feeling? Why do you think I feel this way? What should you do about it?"
Nonverbal communication is something she'll learn about in HS - at least around here they have to pass Communications as a sophomore and they talk a lot about non-verbal vs verbal communication.