You can use matronly to describe a woman who is fairly fat and looks middle-aged, especially if you think the clothes she is wearing are not fashionable or attractive.
...a matronly woman with an air of authority.
matronly in British English
(ˈmeɪtrənlɪ)
adjective
of, characteristic of, or suitable for a matron; staid and dignified in a manner associated with a middle-aged, usually plump, woman
Derived forms
matronliness (ˈmatronliness)
noun
matronly in American English
(ˈmeɪtrənli)
adjective
of, like, characteristic of, or suitable for a matron
; specif.,
a.
dignified, sedate, etc.
b.
having a full figure, graying hair, etc.
Derived forms
matronliness (ˈmatronliness)
noun
Examples of 'matronly' in a sentence
matronly
In a few years that hardness will translate into something matronly.
Pacter, Trudi YELLOW BIRD (2003)
She was a large and matronly RN who had witnessed thirty years of nuthatches and was immune to anything.
Duncan, Robert L THE SERPENT'S MARK (2003)
One matronly woman with a Phyllis Diller hair-do was holding forth on the blessings of gentrification.