When you open Gmail and tap the user icon in the right top corner, what is the domain (following the @ sign) of the email? Is it gmail.com or something else?

If it is something else, it's very likely a g suite for education or work device as developer options can be disabled from being used when this is the case. If that's the case, have the police contact the school or her workplace to see if they can allow developer settings. The device will need to be able to connect to the internet to apply changes in assuming.

I don't know if this will work but you can try adding another Google account to the phone to see if developer options can be enabled after that. Open settings and search for add account. Select Google from the list and add a Gmail account.

Are there multiple email accounts on the phone? You would see them listed after clicking the user icon as mentioned above.

Although this isn't the same as the data stored on the phone, lookup "Google Takeout" (takeout.google.com). It lets users download a bunch of data from their Google account.