It sounds like to me like you attempted to "cut" the pictures folder while the W10 upgrade process was in process of upgrading! Always a bad idea. Copy & pasting=ok; "cut & paste"=BAD.
You seemed to ignore Saltgrasses' question on whether your gf or you backed up her Library (basically her Personal data with documents, photos, music, movies, emails, etc.) to external media. This could be a flash drive, external hdd, Cloud drive as mentioned. I know it's embarassing if neither one of you failed to do this basic step. Not everyone goes to school on computers, and even if either of you took a computer programming class or basic computers, they don't teach you about this sort of thing. Bottom line going forward for you:
"never ever ever hit OK to a Windows upgrade button without having backup to external media--preferably in at least 2 different types of media mentioned!!". This may be a very expensive lesson for the both of you.
Don't mean to chastise you; just trying to educate you. We see hundreds of people do the same thing, and the is the #1 problem people face. They don't ask for help for a computer professional, try to DIY it, and save $$--I get that--but, it's not worth it if you lose all your stuff.
What I suggest now, is that you stop what you're doing, and consider the fact that you may have already screwed the pooch here so to speak. Continuing to try and get that folder back, is more likely to fail than not.
You should turn off that computer, and read our instructions below, and talk to your gf again and ask her if she has that pictures folder backed up somewhere else. Regardless of her answer, it's gone on that computer now. You should take that computer in to your local Computer Pro and pay them to do a Data Recovery to get that folder back, if possible. This will run about $35-$90 the US to do. And if the Tech is proficient, he will do it in 2-3 days. Also, if he can't get it back because you scrambled it too badly, you're not out of luck yet. You can send it out (or your Tech can) for professional Data Recovery; however that's very expensive starting at $250 and takes weeks to do. You'll next have to determine whether those are just random pet pictures and nature landscapes or they contain
IRREPLACEABLE family archive photos for the last 80 years. You and gf have to determine what those are worth.
I happen to be one of the Techs that specialize in Data Recovery, and I've recovered most of the photos from hard drives messed up worse than yours. Typically, professional Data Recovery provides from 70-98% recovery of your photos if done right. If you decide to follow my advice, post back and I'll provide you with the names of the only 2 reliable Data Recovery services in the US that I have personally used.
You and gf have some serious considering to do.
Best of luck and sorry about your mess; I see this on a daily basis now.
<<<BIGBEARJEDI>>>