。
She took care of the poor little bird.
Literal
She [topic-は] that pitiful little-bird's care [object-を] did.
世話をする ('to take care of, look after') is the everyday verb for caring for a person, pet, or anything dependent. The genitive の links 小鳥 ('little bird') to 世話, giving 'the bird's care'. かわいそう ('pitiful, poor, deserving sympathy') is a notable false-friend for English speakers — the か at the start *isn't* the か of かわいい ('cute'); the two are unrelated despite the similar sound. かわいそう conveys 'I feel sorry for it / pity', not 'cuteness'. 小鳥 is a tidy compound: 小 ('small') + 鳥 ('bird').