I need some advice on how to handle something that happened. My older sister and her boyfriend have…

I need some advice on how to handle something that happened. My older sister and her boyfriend have been staying with me cause they got kicked out of the place they were staying. My older sister is almost 2 years sober from heroin and pain pills. Well that being said I think she's still is but I'm not sure. Some of my pain pills came up missing (I was given them after my csection) and I know either her or the boyfriend took them because there the only people that have been in my apartment . How should I confront her. I really don't feel like fighting.