FB buys a shitload of data to 'connect the world' but they don't have to disclose sources unless related to serving ads. They obviously use data sources to make both personal connections and targeted advertising work. While I agree that FB shouldn't tell this user how they figured her family secrets out, they really should let users opt out of all data sources with a button. Currently, in order to opt out you need to go to the sources but nobody will ever know all the sources. This person didn't do much research. Perhaps, rather than contact FB she should have spent time creating her recommended list for a while then opted out from the data providers discussed https://www.facebook.com/help/494750870625830 then she could have done a comparison. Opting out takes a lot of time and I assume it takes a while for these systems to update the opt out information.

I strongly believe that when online companies have a lot of personal information like FB they should not assume users will have a better overall user experience if the service uses offline data that the user doesn't explicitly authorize to be used in conjunction with their online account/profile.