Sister stealing from her sister who is my friend

I recently discovered that my friends sister used stole her sisters drivers license and credit card to rent a car for the weekend. She lost her license from multiple dui's. What do I do since they live togeather?

You tell the sister! Imagine if the bad sister stole your info what would you want someone to do?? If you're to afraid make a fake email account and tell her that way or go straight to the police but this could effect this woman's life FOREVER and the thief needs a wake up call. I know its hard but it has to be done and what happens if something bad does happen and she finds out you knew and said nothing? Not only will you be labeled as a horrible person she could probably sue you..... do what needs to be done..... what you would want someone to do for you if it was your info stolen.