POST EDIT: I worked around it. For some reason, when I uploaded them to the photos section of her memories they didn't appear in the photos section of her memories. I looked at the Gallery from the main Memories tab (not "select from gallery"). From within the Gallery I could find the photos I had uploaded and tag the person in the photo. Now it shows in her memories' photo section.
I'm having this issue today - I have changed files name several times, cropped photos to make it a different size, moved it to a different place on the desktop so it isn't coming from the same folder - still I'm getting the duplicate message on some photos.
Checking the GALLERY is almost always the key to resolution.
it doesn't matter, that you changed the file name or changed the location of where an item is located on you PC.
If FS memories detects that the same file has already been uploaded it will prevent you from uploading it again - even if you changed the name.
Be sure to check your GALLERY - where all your uploaded items are located. and you will probably find the item - that you may have thought never got uploaded, but actually was.