。
She can read well enough.
Literal
She [topic-は] sufficiently characters [subject-が] can-read.
十分 (sufficiently) modifies the potential form 読める (can read). 字 (じ) means characters or letters — 字が読める is the ability to read text, a basic literacy skill. The sentence uses the potential form 読める rather than the more formal ことができる, keeping it natural and conversational.