Her closet is your closet, and vice versa:
One of the many perks of having a best friend is your closet doubles in accordance. Can’t find a shirt to wear to the party? No worries, your best friend has one you can borrow.
If she’s making bad decisions, you either tell her or make those bad decisions together:
There are times when your friend will do questionable things that have the potential to hurt them. Tell them straight up that they’re being stupid, or accompany them on their insane endeavors.