What I think that Velazquez was trying to portray was Infanta Margarita is important and center. I think that because, everyone is looking at her and watching her. Even her off portrait parents. You can see them if you look in the mirror. Another reason for the portrayal is she is dressed so nicely and is being pampered. In that painting you see someone working on her hand. This is all while she is wearing a yellow dress with a flower on the chest.
What I think Pablo Picasso was trying to portray was that the princess was a egomaniac. That's because, she is bigger than her