Jose,

What stands out to me is that she is asking you what you did to your hair (take pills, etc.). This tells me she notices that it's fuller, but isn't sure what you did. When she asked "you're wearing a hairpiece aren't you?" I think it's just another guess of hers. Perhaps her guesses are due to you not giving her an answer, or maybe you react strangely upon her asking you about your hair (I remember how scared I felt when people commented on my hair).

When I first started wearing, people in my family also noticed the difference (fuller hair). I told them I was taking Propecia. Yes, it's a lie, but that satisfied them. They stopped asking. I imagine if when they asked and I would react by NOT giving them an answer, then they would be suspicious. They'll wonder "why isn't he giving us an answer? It must be a hairpiece!", even though the piece looks amazingly real.

The good thing is that they are still wondering. It shows you have a good piece. If you had a bad piece, your sister wouldn't even ask (because she already knows the answer to what you did). My advice for you is next time they ask, tell them you are taking Propecia (or Rogaine, or whatever). If you want to take it a step further, have a bottle of Rogaine visible in your room (in case your sister might be the type that says, "show me the Rogaine").

Good luck! Keep us updated.

Leamon