。
She has very lovely handwriting.
Literal
She [topic-は] writing [subject-が] very skillful [is-です].
字が上手 ('the writing is skilled') is the standard frame for praising handwriting. The intensifier とても ('very') boosts the praise, and the polite copula です fits a register where the speaker is being courteous — perhaps complimenting an acquaintance or speaking respectfully about someone. とても is the standard polite intensifier — neutral, useful in nearly any context. The な-adjective 上手 keeps the slightly formal feel; in more casual peer-level talk one might hear うまい instead.