How can I get her phone working again? Is it just as simple as changing apple ID and logging her into phone again?
If the person who has her information has changed the Apple ID password, you won't be able to sign out of the old ID.
See if you can change the password and see the compromised link.
You might want to consider changing your password and making sure it is a strong one. You can also add 2 Factor Authentication to your account for more security. If the attempts continue, you might want to consider a name change.
Link to contact Apple Support in the article.
Apple ID has been compromised.
Note the restrictions in the article.
What to do after you change your Apple ID or password - Apple Support I suggest doing this before you change your Apple ID or password.
Apple ID -Two-factor authentication
Two Factor Authentification availability.
2 Factor Authentication - How to generate a recovery key
Apple ID - Using app-specific passwords.
My mom's elderly and has comprimised her apple ID. Someone has all her apple ID, password, and securtity answers for apple ID. Now she's not able to dial out on her phone.
