Rubenesque suggests to me, also, many pounds overweight. Matronly sounds as though it could cover fat, as belm' suggests, and even medium-sized women. I can imagine a skinny, matronly woman, too. Correct me if you think that matronly women categorically cannot be skinny.

But portly implies some degree of dignity--and I can't limit that adjective to men. My imagination easily configures a roomful of portly women, none of them necessarily matronly, but many of them Rubenesque behind the curtains, so to speak.