Can't group message with iphone imessage to imessage on ipod touch.

My friends has an iPhone, and she sent out a group message to all of our friends. I have an iTouch 4th Generation, and thought that if she typed in my email instead of my phone number, it would go to my imessage account on my iTouch. However, when she sent out the group message, it went to my email inbox. How d I make sure, when she sends out a group message, that is goes to my imessage account on my iTouch and not my email and not my phone?