。
She writes much better now than she used to.
Literal
She [topic-は] before [than-より] much better characters [object-を] writes.
より marks the standard of comparison ('than X'); ずっと ('much more, by far') intensifies the comparative — without it the sentence would just say 'better than before,' which feels noncommittal in Japanese. 字を書く is the canonical phrase for 'to write characters,' closer to English 'write [in handwriting]' than to general composition. The improvement might refer to penmanship (more typical) or to writing skill more broadly.