UP TO A NEW CHALLENGING QUESTION?

Some of you have given the right answer to last week's question, but answers given in the corridor between classes don't count, so please write it down on the blog!
Here's a new question for this week and, since the last one is still unanswered, the new one is, once again, about family:

3. A woman gives a beggar 20 cents. The woman is the beggar's sister but the beggar is not the woman's brother. How is this?

Thanks beforehand for taking part and don't forget to write your answer in your best English; remember any good text is worth an extra good mark.
Good luck or better to say, good lateral thinking!