AND THE WINNER IS...
Her phone had my number, and her own too, selected
Thank you all for replying, I think everyone was 'nearly right'
OYSTR said:Go to Settings>Messages>Send & Receive and check the "you can be reached at" addresses making sure only your contacts are listed. Uncheck the ones that are not you. Turn off iMessage and then turn back on.
Do the same at Settings>FaceTime>You can be reached at. Turn off FaceTime and then on again.
And then maybe a hard reboot (power and home button held down) for good measure.
Her phone had my number, and her own too, selected
Thank you all for replying, I think everyone was 'nearly right'