@123MaeStar456 Just to be clear, are you saying your saves have disappeared, and now you only see your sister's saves? Or is this about the Gallery, or something else? Do you and your sister share a computer, and if so, do you share a user account on that computer?
Please also let me know whether your computer runs Windows or macOS/
@123MaeStar456 Is OneDrive running on your computer? If so, and if you and your sister share a Microsoft account, OneDrive may have downloaded your sister's files to your computer. It would be unusual for your files to be deleted at the same time, but perhaps the problem is that the saves had the same names.
At any rate, please login to onedrive.com and look for your missing saves. You may be able to distinguish them by their modified dates, or they may have names that show they're from your computer and not your sister's. If you find any, you can download them back to your device. Make sure they have the proper format: Slot_ followed by an eight-digit hexidecimal (0 to 9, a to f) number followed by .save , possibly with a .verx on the end. Any extra characters should be removed.
Please also check your saves folder for any improperly-named saves. These may be your own saves but renamed to distinguish them from your sister's. If you need more help with the renaming process, please see this:
Other than OneDrive or a similar service that syncs files between computers, I can't think of any reason your sister's saves would have shown up on your computer. Sims 4 doesn't support cloud saves, so the only copies are stored locally on the computer.
