What do I have to look for on her drive to assess if it can be done or not? (Too late for system restore)
She is an hour away so trying to see if it is possible before asking her to drive all the way here.
I can use Teamviewer to look on her hard drive, etc..
I hate to quote other forum content but this one is invaluable. You mean rollback to previous Windows version (7 or 8.1)?
Courtesy of Windows 10 forums it would have to be subject to the following:
"When you upgrade to Windows 10, a copy of the previous installation is saved to the Windows.old folder in the root directory of the Windows 10 drive as a backup. This backup will allow you to be able to go back to the previous build of Windows for up to 10 days after upgrading to Windows 10 if you should want to.
To go back, you'll need to:
You will need to have enough free space on the Windows C: drive. Usually the free space needed is at least twice the size of the C:\Windows.old folder.
Keep everything in the Windows.old and $windows.~bt folders after the upgrade. This means to not delete these folders, and not check the Previous Windows Installation(s) box when using Disk Cleanup.
Know the password you used to sign in to Windows 7 or Windows 8.1 (if you used one).
Have the USB drive you used to upgrade to Windows 10 (if you used one).
What you need to know before you go back:
It will keep your documents, photos, and other personal files, but it can't save:
Any apps installed after the most recent upgrade
Any changes to personal settings made after the upgrade
If you're using a local account, you'll need to sign in to this PC with your old password after going back. This doesn't apply to a Microsoft account.
If you go back to Windows 8.1, some apps that came with Windows, like Mail and People, might not work anymore. To fix them, reinstall them from the Store.
If you’re a Windows 10 Insider with a Windows 10 preview build installed, going back to an earlier build won’t remove you from the Insider Program. When the next preview build is ready, it'll be installed on your PC."
If you are referring to our Windows 10 Rollback Utility, the chances that you can remotely tell if it's usable are slim. If you can boot into Windows, you don't need the tool... and if you can't boot into Windows, then you can't remote into her PC to determine if the Windows.old directory exists in the root of the C:\ drive (which EasyRE/W10Rollback use to roll back a failed Windows 10 upgrade).