Hi there,
You don't say which version of Win10 you attempted to upgrade to? Is it Win10 Home or Win10 Pro?
If you attempted to download the Win10 Home ISO file, and install it, it will fail as that is not a legit upgrade path.
Win7 Ultimate has no equivalent upgrade path (i.e. to Win10 Ultimate), as Win10 Ultimate doesn't exist, so therefore you would need to Win10 Pro. If you downloaded the correct ISO file from Microsoft, you have to create a separate Disc or USB stick for each version in either 32bit or 64bit configuration. Is your Win7 Ultimate a 32bit or 64bit? If you don't know about this or didn't know how to find it, that can be yet another problem. If your Win7 Ultimate is 32bit and you downloaded and created a bootable install disc or usb stick with 64bit; it will always fail. You would need to create a bootable install disc or usb stick with 32bit Win10 Pro in that case. Or vice-versa if your Win7 Ultimate was 64bit. You would also have to make sure your computer is the correct CPU type as well. (you can type the keyboard combo
*Windows-logo-key+Break key* to bring up your system details windows). This is most likely where you went wrong. The above items are also what cause so many home users to fail when they try to DIY a Win10 upgrade!
Furthermore, just so you know, creating a bootable Win10 usb stick with the correct ISO file is no easy task. It took me 6 months in order to figure it out and I've been doing computers for 45 years!! I would stick with trying to burn your ISO file to DVD disc if you have a burner on the machine you are trying to upgrade, or access to a different computer with a DVD burner on it. This is way easier to do.
Those are about 6 ways you might have done your upgrade incorrectly, and if you get really frustrated I suggest you consider taking your girlfriend's computer to a repair shop that employs licensed Techs to do the work (make sure they have an A+ license or better). The upgrade will cost from $50-$150 in the U.S.; could be 2-3 times that if you live outside the U.S.
Best of luck to you,
<<<BIGBEARJEDI>>>