That line by Duchesse de Polignac about how "the servants take over the house" seems pretty prophetic when you realise the context.
Marie Antoinette is standing naked in her cold bedroom when her sister-in-law, the Countess of Provence walks in. As the woman with the highest rank in the room, the priviledge of handing the Dauphine her clothes goes to her. She sees that Marie is cold and shivering, but still takes a long time to take off her gloves. Why? Possibly because historically, the Countess did not like Marie Antoinette and at all and made no secret of the fact that she believed she and her husband would make much better rulers than Marie Antoinette and Louis XVI.
Fridge Logic: With all of the cake that the court, especially Marie Antoinette, eats - wouldn't you expect them to be fatter?
Some ladies were actually pretty plump.
And we only have paintings to go on- a an artist on commission is hardly going to make his employer look frumpy.
In truth, Marie-Antoinette was rather a light eater, and before her first child's birth, she was a very active dancer, spending most of her nights at balls, which may have helped with losing some weight.