Friend thinks I should be concerned

My friend thinks I should be concerned because she found hotel keys in my so coat pockets. She lives with us now has for about a week. However, my so is a conductor for Union Pacific and travels between home and another city hauling freight and keep the train safe. He has a mandatory 10 hour break once he gets to the other city and has to stay at oak tree inn. I've explained this to her and she blantly ignores me on it and has started arguments with my so in front of me. Idk what to do honestly she's been my best friend for years, but her isn't acceptable lately. Am I over reacting?