You said to me, "She is my sister".

In changing the given sentence from direct speech to indirect speech, we need to follow the rules of reported speech. Here, the reporting verb is "said to," and we need to adjust the sentence accordingly:

The original sentence is in direct speech: "You said to me, 'She is my sister.'"

In indirect speech, the reporting verb "said to" is changed to "told," and the pronoun references need to be adjusted to reflect the perspective of the speaker. Here, "you" changes to "me" and "my" changes to "your":

So, the correct transformation is: Option B: You told me that she was your sister.