What should I do with the money I took from my uncle to help a girl who claimed to be an orphan and in need, then I discovered she was a fraud, and my mother spent this money?

You made a mistake by giving the money to your mother, because your uncle did not intend his charity for your mother, and an agent does not act contrary to what his principal intended. If the agent acts contrary, then his action is subject to the principal's approval or rejection. You must inform your uncle of what you did. If he forgives you, then so be it. If he demands the money from you, then return it to him because you are liable for the money due to your transgression. Do not dispose of the money except with the permission of its owner (your uncle). If you cannot inform him, then return the money to him by any means that reaches him, so that he knows it is his money, even if he does not know that it came from you.