。
She took care of her aging mother.
Literal
She [topic-は] aged mother [possessive-の] care [object-を] did.
老いた (おいた) is the past/attributive form of 老いる ('to age, grow old'), used as a prenominal modifier — 'aged/aging mother.' 世話をする (せわをする, 'to take care of, to look after') is one of the most essential caregiving expressions in Japanese.