The correct option is
B has long hair
In the given sentence, the subject is being given the quality of possessing long hair. Thus, the verb in the answer must indicate possession and also, it must agree with the third person singular pronoun 'She'.
Option A is incorrect. 'is long hair' indicates that the subject is given the quality of being long hair. This, does not make any sense. Thus, it is incorrect.
Option B is correct. 'has long hair' indicates that the subject is given the quality of possessing long hair. Also, 'has' is a third person singular verb. Thus, it meets the required conditions and is the correct answer.
Option C is incorrect. In 'have long hair', 'have' is a third person plural or a first person singular verb. Thus, it cannot be used for third person singular pronoun.
Option D is incorrect.In 'have long hair', 'have' is a third person plural or a first person singular verb. Thus, it cannot be used for third person singular pronoun. Further, an adjective should be placed before the noun that it modifies. Since here that is not the case, the phrase is grammatically incorrect.