。
She seems very happy.
Literal
She [topic-は] very happy [seems-そう].
~そう attaches to adjective stems (here 幸せ) to express 'looks like, seems' based on appearance or impression. The two main 'seems' constructions diverge by source: ~そう (looks/seems) draws on direct sensory impression; ~ようだ leans on broader inference; ~らしい reports hearsay or general appearance. Conscious selection among these is part of intermediate-Japanese mileage.