Her presence sensor shouldn’t have anything to do with it. I agree, I would suspect other environmental changes caused by her visit, in particular just greater use of Wi-Fi. If she’s watching a streaming box, using Wi-Fi on her phone, and running Wi-Fi on a tablet or laptop all at the same time that’s adding a lot of potential local interference that could affect zigbee devices.
Have you checked the channels on your smartthings hub and Wi-Fi router for potential interference?