I'll tell you how I did it for my son. It might seem a little mean but he NEVER stole anything ever again. I had a police officer pretend to catch her and said she was going to jail for stealing and even started walking him to the police car. My son was so scard I'm sure if he had to pee he would be peed his pants. He cried and said he was sorry an said he'd never did it again. The police officer got down on his knees so he was eye to eye with my son and told him if he promised never to steal again he would let him go this time with a warning but the next time he was going to jail. I'm telling you I wanted to cry for him cause he was so scared but he had to learn there are consequences for your actions. Today my son is in the Marine Corps and he never stole anything again. He remembers it as well.
I know what I would do .. let the punishment fit the crime...if this was a behaviour I couldn't control with just general threats or typical punishment .. I would resort to a few of my friends who are policemen .. I'm thinking they could get the point across quite clearly about the consequences of stealing.
Steal her stuff. Taking away her toys or favorite stuffed animals will show her how it feels. Explain to her that the way she feels when she losing her things is how she is making other people feel. She probably doesn't understand how it makes people feel when she does it so this will show her why its wrong.
Find out from her why she is doing this. At age four, if she is intellectually normal, she will have reason(s) For her stealing. When you have the reasons, you will know the solution. Please don't hit her. Punishment doesn't work. Building rage into a four-year-old guarantees you a miserable future.