My wife had a problem with a girl creating a facebook account using a similar email to hers that somehow got her gmail account connected to that facebook accoun

My wife had a problem with a girl creating a facebook account using a similar email to hers that somehow got her gmail account connected to that facebook account. There was some account sharing going on, as the girl used that email address to login to her facebook account and all the FB notifications ended up in my wife's inbox. At first I thought her account was compromised, but it was a secure password, so it seemed to be caused by the only slightly differing email addresses somehow being shared internally by gmail. Only after activating 2-factor authentication did I manage to prevent that girl from using my wife's gmail account. However, this was followed by a few weeks of constant gmail notifications about a detail/password change request sent to her phone.