Baby plays the blues

Grandma and Grandpa came to visit today and Pumpkin A took right to them again like it hadn't been months since she had last seen them. She enjoyed playing with them and eating with them. She even started to play on her piano while sitting independently. She had a wonderful but exhaustingly fun day. However, whenever we tried to take her picture at the piano, which she smiled and squealed at playing, we got this expression. Not sure what it means but I think she wanted to focus on her music right now.