。
She took care of the baby.
Literal
She [topic-は] baby [possessive-の] care [object-を] did.
世話をする (せわをする) is a set phrase meaning 'to take care of' or 'to look after.' 世話 means 'care, looking after, assistance.' This expression covers a broad range of caregiving — from feeding and changing diapers to supervising and keeping someone comfortable. The related expression お世話になる ('to be indebted to someone for their care') is one of the most important social phrases in Japanese.