Characters
I’m a woman, Mary. I can be as contrary as I choose.
— Dowager Countess ‧ Downton Abbey

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker asserts that being a woman entitles her to be as contrary as she likes, and addresses Mary directly. The line is imperious yet playful, treating stubbornness as a privilege she has claimed and has no intention of justifying.
Context reviewed