If it was truly a gift, the answer is no. It's your money and no one has the right to demand it. However, there are "gifts" and there are "gifts." Did your mother intend for you to hold the money in case she needed it? Did she intend for you to share it with your siblings? Was she totally competent when she made the gift? Was the plan for you to use it to pay for school tuition, but then circumstances changed? Of course, I’m just making these situations up, but the point is that circumstances may give the estate a legal or moral claim on the money even if it's ostensibly an outright gift.