I would have to agree with this. You might consider sitting down with your sister, and talk to her about why she asked you to be her maid-of-honor; and what she expects from you. After you put her on the spot and she responds, you could tell her that it is the nicest thing that could have happened to you; and you love her for that. If she were to mention that she knew that you were a CD, then you could talk about it; other wise don't mention it as what was mentioned before, it might spoil her day.