Set up new iPhone with iCloud backup without access to the old phone

She just needs to sign into the same iCloud Apple ID and then turn on the information that she had been syncing with iCloud. If she made an iCloud backup, she can also use that backup to setup the new phone during the setup procedure. If she has already setup the phone, then she also has the option to restore from an iCloud backup from that point, following these steps. Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Good idea. You are going to have to erase* the iPhone and then start over and set it up again using the iCloud backup.

• When you do this, there is an option to keep the carrier info, etc.

She needs to log into the iCloud that was on her old phone and enter the backup that was on her old phone. You could try to get her old phone to restart with 3utools.