If you can't find it, it might be a good idea to help your mother setting up a good backup scheme. As we say here, you only lose what you didn't backup.
1000 images is 1 to 2 GB. A folder with 1.5 GB isn't too difficult to find use TREESIZE FREE (free download). But that only works if she didn't press shift-delete by accident.
my mother was working with her documents, when one of her folders containing around 1000 images disappeared. I tried to find the folder as well as the images in it without any success. The box "show hidden folders" is checked. I tried even Recuva to scan the recycle bin - nothing. Now I am running the Recuva's deep scan, but I doubt it helps. Does anyone have an idea about what could have happened with that folder?