。
She's stubborn.
Literal
She [topic-は] stubborn is.
強情 is a na-adjective with a slightly negative tilt — somewhere between 'stubborn' and 'pigheaded.' It's softer than 頑固 ('hardheaded'), which often gets used affectionately for a stubborn old man, and harsher than 意地っ張り ('willful'), which tends to apply to children or a temporary fit of pride. The polite copula です here lifts the register from the bare casual 強情だ; the sentence reads as a measured judgment rather than a complaint thrown at the person.