you sound like my little sister. You know something, what your experiencing right now, this is also a great blessing, your mother is not just crying with sadness but also with happiness, its kind of a mix-up feeling which almost every mother has and its natural. Think about it if you were at her place it would be really hard for you too. Its really great that she is able to express her feelings and show her love to you. There are times when our parents become cute little kids ageing no more than 2-3 years old and we have to up lift their spirits as if we are their elders. Now its ur time to be her elder and make her feel more happy, and try to be happy yourself that Allah has given you such a great moment of your life to be shared with your family and your love one. Just try to think positive and be happy.