Send me a PM when your sister joins with her username.  Please be advised though, that if you are going to play against your sister, she cannot continue to play on your account.  Also, some suggestions for playing against a relative from the same house/computer:
- Do not play team games on opposite teams, play on the same team.
 - If you are going to play large non-team games against one another, let the other people know that you are related or play private games where people know that you are related.
 - If one person is a lot better than the other, try not to play 1v1 games, as it may be seen as throwing games.