I don't think it's a doll but I do think something went on that day.
She wasn't expected at that Polo match, she just turned up looking bedraggled, frazzled and thrown together.
She apparently wasn't prepared for a day in the sun with a baby. no sunhat, no protection for him and she looked totally uncomfortable with Archie.
That couple are Anneke and Charlie Gilkes. Charlie is a close friend of William, Harry and Eugenie.
He went to Eton with Harry and dated Pippa Middleton. They all attended each others weddings, though W & K didn't attend his because K had severe morning sickness and W had a prior engagement.
Going off piste here.. All the Middletons were at his wedding, have you noticed the Middletons get invited everywhere as a group, they come as a package.
Reports I have read said that she just turned up, then paced about looking angry. A bit like Tom Inskips wedding.
Something happened that day but I don't recall any rumours of exactly what.