The correct option is D is she?
A question tag is a short question at the end of a statement. It changes
a declarative or imperative statement into an
interrogative one. They are mainly used to confirm something or
encourage a reply from the listener.
The question tag is like a reverse
of the sentence, it starts with the verb and ends with the subject.
Hence, the question tag that follows a positive statement will be
negative, and vice versa. The verb is generally the same as in the
sentence.
In the given sentence, the verb is "isn't", which is negative. It's the contraction of 'is not', hence the question tag formed will be positive, i.e., 'is she?' and option C is correct. 'Will she' is used as a question tag when the verb in the sentence is 'will'; 'isn't she' is a negative question tag used for positive sentences and 'has she' is used as a question tag when the verb in the sentence is 'hasn't. Hence, options A, B and D are incorrect.