Math Puzzles & Logic Problems

Last vacation, my cousin came over to stay at my home. We made the most of her stay at my place... and I even earned a few chocolates. Everyday, we would play a game of chess. Whoever lost the game owed a chocolate to the other. After the last game we played (that was the day she was to leave), we counted the number of games each of us had won and lost. Wow! I had won more than her. So, she handed me 18 chocolates... though she herself was the winner in 9 games. How many days did my cousin spend at my place?