Answer:
(She will visit us this year,) won't she?
Explanation:
Basically, question tags are short lines added to a sentence (declarative or imperative) in order to make it a question.
They are in the same tense as the main sentence and if the sentence wa negative, question tags will be affirmative and vice versa.
Also, when constructing a question tags, we make an inversion (a change of place of subject and a verb).
So, with this in mind, let's examine the sentence above:
She will visit us this year.
Subject is she, verb is will. The sentence is affirmative.
So, for a proper question tag, we must change the verb into negative form (will --> won't) and make an inversion:
She will visit us this year, won't she?