She should’ve closed that bank account the second she turned 18.

Teenagers don’t always have as much financial independence as they ought to. They often can’t open a bank account without their parents’ name on it, which is all well and good if your parents are good stewards of your money. If your parents don’t care about doing right by you, they might steal from you because you’re a teenager who doesn’t have the resources to stand up for yourself and get your money back. Children lack property rights, so while it’s morally wrong to take money that your teenage child earned by working at their job, the law is not going to side with the minor. 

Once you’re an adult, you can create your own bank account to ensure that nobody else can ever have access to your hard-earned cash ever again. If someone repeatedly proves that they cannot be trusted not to steal from you and you don’t do anything to stop them from stealing, you can’t be surprised when they keep doing it again and again. They aren’t going to change if you keep letting them get away with their bad behavior without consequences.