The tool you use to download a copy of your Facebook data isn't very obvious at first. On the "General" section, select the option to "download a copy of your Facebook data." My data didn't include phone numbers for relatives who are not on Facebook — but you said the website collected your grandmother's number. Anyone should be able to view their invite history data by clicking here. Have more questions about your Facebook data?
Source: CNN March 27, 2018 14:37 UTC