。
She was feeling a little better yesterday.
Literal
She [topic-は] yesterday a-little condition [subject-が] was-good.
具合 ('condition, state') paired with がいい/が悪い is the standard frame for talking about physical wellbeing — 具合がいい for feeling well, 具合が悪い for feeling unwell. The same word also describes the state of machines and equipment ('working / malfunctioning'), so 具合 is broader than its English equivalents. The implication of 少し具合がよかった is comparative — she's typically been less than well, and yesterday brought a small reprieve. Without that backdrop the sentence would sound oddly hedged.