。
I don't think she's happy.
Literal
She [topic-は] happy is-not [quotative-と] think.
Note the negation placement: in Japanese, 幸せでないと思う means 'I think she is not happy' — the negation belongs to the embedded clause. Contrast with English, where 'I don't think she's happy' shifts the negation onto the matrix verb. Japanese keeps it scoped to where it semantically belongs. The form 幸せでない is the plain negative copula attached to a noun/na-adjective; the polite alternative would be 幸せじゃありません.