Am I right or wrong?

So my parents give my sister some money to hold for an emergency like to pay my half of the rent and for food and so on. So I recently saw my sister using the money for nonsense like buying new shoes and she already have a lot and for house hold stuff and food for her best friend who has his own money and can buy it from his self. One day I decided to check how much money was left back and I noticed she spend over 500 EUR in less than a week or two. I got a letter the next day and my sister and I had an argument cause she was suppose to get 50 EUR from me from that letter so I told her I am not opening it now and she get on about how she isn’t going to help me no more and so on, but she never really did help me with anything I would have to beg her to help. So now she isn’t talking to me cause I took the money and bank it not only cause she is spending it badly but also because I need medicine to and if there is no money I can’t get my medicine. She is almost twenty years old and is getting money but can’t seem to help no one but herself.

Am I wrong for taking the money, do I talk back or leave her alone?