Can some one explain how the answer choice can be correct when the pronoun 'her' clearly does not have a antecedent?

the nouns in possesive case can be an antecedent to the possesive pronouns only!!
and her is a possesive pronoun!
thus her clearly refers to the governor

The singular subject in the original sentence, "the governor's team," agrees with the singular verb
phrase "has not been."

(A) CORRECT. This choice is correct as it repeats the original sentence.

(B) The subject-verb relationship is incorrect. The singular subject of the sentence, "the governor's
team," does not agree with the plural verb phrase "have not been."

(C) The subject-verb relationship is incorrect. The singular subject of the sentence, "the governor's
team," does not agree with the plural verb phrase "have not been." Also, the subject pronoun "she"
has no antecedent. The subject pronoun "she" cannot refer back to the possessive noun, "governor's."
Only possessive pronouns, such as "her," can refer to possessive nouns. Finally, the phrase "her
proposal on controversial education reform" changes the original meaning. This phrasing implies that
the education reform is controversial. However, it is clear in the original sentence that it is the
governor's proposal that is controversial, not education reform itself.

(D) The subject pronoun "she" has no antecedent. The subject pronoun "she" cannot refer back to the
possessive noun, "governor's." Only possessive pronouns, such as "her," can refer to possessive
nouns.

(E) The subject pronoun "she" has no antecedent. The subject pronoun "she" cannot refer back to the
possessive noun, "governor's." Only possessive pronouns, such as "her," can refer to possessive
nouns. Also, the phrase "her proposal on controversial reform in education" changes the original
meaning. This phrasing implies that the education reform is controversial. However, it is clear in the
original sentence that it is the governor's proposal that is controversial, not education reform itself.
Finally, the phrase "to make comments" is not as concise as the original "for comment."

Rule: On the GMAT, every pronoun must have a noun antecedent in that sentence. The antecedent need not appear before the pronoun, but it must be there in noun form.

In E: "she" is trying to refer back to the governor. Unfortunately, there is no noun form of "governor" in the sentence. Instead, we have "the governor's team of advisors" where the word "governor" is in the possessive tense and serving to modify the subject of the sentence: team.

Other examples of this "possessive poison" error:

"I bought Jose's birthday present yesterday, but I never got an invitation to his party." --> Here "his" is trying to refer to "Jose" but cannot legally do so. Fix: "I bought Jose a birthday present yesterday, but I never got an invitation to his party."

"Nobody knows why he dresses this way, but Steve's signature wardrobe is a black turtleneck with jeans and tennis shoes." Again, "he" is trying to refer to "Steve" but cannot do so because "Steve" is not present in the sentence as a noun.