。
She had a dress made for her.
Literal
She [topic-は] dress [object-を] received-the-favor-of-making.
~てもらう reframes what English calls 'had X done' as receiving a favor. The unmentioned doer — a dressmaker, a friend, someone — gets quietly elided because Japanese keeps the spotlight on the speaker's side of the transaction. This pattern lives inside the broader 授受表現 (giving/receiving) system, where every action is mapped onto in-group / out-group flow: あげる (give outward), くれる (give inward), もらう (receive).