Stubborn, stubborn girl

My daughter wins the prize. This 16 month old little girl is so stubborn. As I type, we are in the middle of a face off. Emily is our 3rd child. So I know from experience, she is capable at this age, of communicating. We have signed with all 3 of our kids. Once I was sure that Emily knew how to sign "all done" and understands what it means, I require her to sign it to me before she can get out of her high chair. I believe this teaches her to communicate constructively rather than just scream, holler and yell to make her requests known. But she chooses to not communicate with me at the moment. She would rather sit in her high chair and scream than sign "all done" and get down. This is about the 4th time we've had a stand off like this. You'd think she'd learn by now! I ask her, "do you want to get down?". She shakes her head no. When I sign and say "all done", she turns her head away from me and sticks her thumb in her mouth. So I go about my business, fixing lunch, cleaning up the kitchen, posting on my blog. But when I leave the room is when she gets really upset! Eventually she will sign it. It's a battle of the wills. I will surely win.