。
She's been feeling much better today.
Literal
She [topic-は] today [contrast-は] all-along condition [subject-が] good.
ずっと has two flavors: 'continuously, the whole time' (temporal) and 'by far, much more' (intensifier). The temporal reading dominates here — 'all day she's been doing well.' 具合 is essentially synonymous with 調子 when describing how someone feels, but 具合 leans medical/physical, while 調子 covers a wider range of states. The contrastive は in 今日は again backgrounds an unspoken comparison: she wasn't doing this well on previous days.