。
I hear she used to be a model.
Literal
[topic-は] model was [hearsay-そうだ].
~そうだ here is the hearsay marker, distinct from the visual-evidence そう that attaches to verb stems. The hearsay そうだ attaches to the plain form (here, the past copula だった): モデルだったそうだ ('I hear she was a model'). The construction is the standard way to relay information learned from a third party — a friend, a news article, or rumor.