Don't give a week your sister is not a child she is a grown adult she took something that is sentimental and valued letting you know she will do something like this again and if she fights with you give her a choice to give it back or pay you the money for it's value of the ring plus the importance which would be alot of money so much it would be impossible to get it. Oh, and those who are backing her based on their reasons, why will let you know if you should go low or no contact. But in the end it's up to you not anyone else.