The correct word to use in the sentence is "whom."
"Whom" is the objective case of the pronoun "who," which means that it is used as the object of a verb or a preposition. In this sentence, "whom" is the object of the preposition "to."
The sentence is asking whether a specific lady is the one that the speaker had planned to visit. Since "whom" is used to refer to the object of a preposition, it is the correct word to use in this context.
To summarize, the correct word to use in the sentence is "whom" because it is the object of the preposition "to." The other options are not appropriate because they do not serve as the object of a preposition.