What an excellent McGonagall!
I think it is simply a younger McG. . .perhaps when Arthur Weasley was a first year or something.
I can see, though, that she is certainly going to age into the Minerva we all know.
She looks a bit frazzled. I wonder what that potion in her goblet is. No doubt, Horace Slughorn brewed it for her, perhaps to calm her nerves.
-- I love the hat.