I would have a chat with your mum..let her know how you feel that your sister is the favourite as she gets help and you, who are sensible , do not. Explain how you feel that she is not helping your sister to manage money...and perhaps this would be preferable to chucking more money at her. Then , if I were you, I would sit back smugly and smile about how much more mature than my sister I am. You are an excellent money manager...your sister is not...I wonder if that has always been the case. Well done you...you should be proud of yourself. Do have a chat with your mum though......