All 4 Uses

assert
in
The Great Gatsby
(Auto-generated)

I waited, and sure enough, in a moment she looked at me with an absolute smirk on her lovely face, as if she had asserted her membership in a rather distinguished secret society to which she and Tom belonged.
p. 17.6

asserted = said (that something is true)
Her body asserted itself with a restless movement of her knee, and she stood up.
p. 18.1 *

asserted = was forceful
"I've done some nice things out on Long Island," asserted Mr. McKee.
p. 32.5 *

asserted = said
Her laughter, her gestures, her assertions became more violently affected moment by moment, and as she expanded the room grew smaller around her, until she seemed to be revolving on a noisy, creaking pivot through the smoky air.†
p. 31.1

Definitions:

(1) (assert as in: asserted her opinion that...)
to say that something is true -- especially something disputed
(2) (assert as in: asserted her authority)
to be forceful in exercising influence or rights
(3) (meaning too rare to warrant focus)