My mom comes to visit me 5 months out of a year. I have realized she is stealing from me. How do I deal with this?

I found my stuff in her bags. So I confronted her. I didn't want to make a big deal, so I just told her what I found in her bag and to please just put it back. She left to go back home and I realized she stole from me again. How do I deal with this? She is 83 years old.