。
She did her hair for the party.
Literal
She [topic-は] party [genitive-の] [for the sake of-ために] hair [object-を] arranged.
整える is the verb of choice for putting something into orderly, presentable condition — hair, clothes, a room, a document. It's notably more polished-sounding than セットする (the loanword for 'doing one's hair') or 直す ('fix, straighten'). ~のために here marks beneficial purpose ('for the sake of the party'), distinct from causal ~ために ('because of'). Hair is treated as a presentation artefact in Japanese in much the same way English speakers think of 'doing' or 'styling' it.