ex wife stealing money from my step daughter

Hi I have a stepdaughter and recently she just complaint to me and my hubs about her mum have been stealing money from her piggy bank that she have been saving from a full to empty. She use my stepdaughter money that was given from me my husband and my mil and her mum would use that money to buy her cigarettes, her makeup, and her engagement ring that the boyfriend couldnt afford to pay for. Stepdaughter said her mum have been doing this for a long time and she thought her mum put it inside the bank but Nope. Cos her mum is.doing off and on jobs. And her mum doesn't save money at all, she always go out and eat or to treat her bf to eat