See if you can recover the ID/password. Use every email address you can think of.
Apple ID - How to find your Apple An iCloud e-mail address is an Apple ID.
Apple ID - Find
If you forgot the Apple ID password, enter the Apple (iCloud) ID, and click Forgot Password. See if you can get an email option if necessary.
Apple ID - Manage
Apple ID – Forgot Password
You need to change/add the number on her Apple ID. After the change, allow up to 24 hours for the change to sync. Before trying to make the change, sign out of Messages/FaceTime on all devices/computers.
Apple ID - Manage
If you need a verification code, see if anything here helps. If necessary, you can use account recovery as explained in the link at bottom of the article.
Verification code - how to get one and sign in with two-factor authentication.