Is there a way to confirm that someone has deliberately opted out of BT WIFII rather than by default ?
Everyone by default is opted in to BT WiFi, you have to request to opt out.
Is it that your mum is using BTWifi from one of her neighbours BTWifi signal? If that is the case the neighbour can opt out at any time and that would stop others from using it.
It could also just be that their BT Hub is needing restarted. BT can not do this but if she knows whose BTWifi she was usng she could ask them to restart their hub. They of course are under no obligation to do that so the may decline to do it.