What is a proper punishment for a 6 year old who stole something from a family members house and then lied?

My 6 year old daughter stole something from my sister-in-laws jewelry box. I found the item 3 weeks later and confronted her. She attempted to lie but eventually admitted. I made her call my sister-in-law and apologize. This is not the first time she has taken something from someone's house. I don't know what to do to make her understand the severity of her actions and to impress upon her how lying will only make it worse. Please help.