Not sure if this will help because your post lacks info (type of router, for starters) but you can try this on your sister’s iPhone;

Tap on the Settings app, go to Wi-Fi. Tap on the little i icon next to your wifi network name. Check the Private Wi-Fi Address setting and make sure it is set to Fixed. Then see if the disconnects still happen. If no change, change it to Off and test again.

This post has been edited by dev/numb: Jun 28 2025, 09:37 PM