Well, she is wearing a bustle which makes the rear end quite bulky under the jacket...although I do understand it's not the rear that shows a bun in the oven

...on the other hand, she may have just had a baby and not yet regained her figure.
On the third hand, that outfit is pretty bulky. The lady on the left looks a bit bulky, too.
There, wasn't that helpful?

Cheers,
C