Is it normal that my little sis keeps stealing from me?

Me and my lil sister are 9 years apart. She is a teenager. Every time I stay with my family for an extended period of time she always gets into my possessions like makeup, clothes, accessories and secretly steals them.

She knows better not to because I have expressed to her many times that I don't want her touching my stuff. She knows this very well too and what the consequences are. But I always find the stuff later, like from her bag and purses and I get really upset/emotional/disappointed because I keep trusting her, and she keeps deceiving me.

I know this happens between siblings, but I think my lil sis has a major stealing problem. When she was younger she even stole money from my parents and an ipod from her school. When me and my parents lecture her, she sobs and seems to really get it only to relapse and do it again. What should I do to make her understand?