The elderly woman had the servant go fetch the trunk.
Literal
Elderly-woman [topic-は], servant [to-に] trunk [object-を] fetch [purpose-に] go [causative-させた].
~させた is the causative: the woman caused the servant to go. 取りに行く uses the purpose-motion pattern (verb stem + に + 行く). 召し使い (めしつかい, 'servant') is old-fashioned vocabulary from an era with household servants.