"<u>She</u>" is a personal pronoun that replaces someone mentioned in the sentence, in this case "<u>Mrs. Wilton"</u>. The personal pronoun "she" is acting as the subject of the subordinate phrase and makes reference to "Mrs. Wilton". Personal pronouns acting as subject cannot replace other pronouns.
The rest of the option are incorrect since the pronoun "she" does not replace the noun market, the noun daughter or the object pronoun "her".
