。
She's gradually getting better.
Literal
She [topic-は] gradually [is-getting-better-良くなってきている].
良くなる ('become good, improve') is the foundational change-of-state pattern for the i-adjective いい/良い: いい→良く→良くなる. Adding ~てくる ('come to / develop into') gives 良くなってくる ('become good and continue to,' i.e. 'gradually improve'); finally ~ている marks that gradual improvement as ongoing — 'is currently in the process of getting better.' Three layers stack to deliver fine-grained aspect: change → development-toward-now → ongoing. だんだん ('gradually, little by little') reinforces the pace.