lillyelephant101 The fact that OneDrive overwrote all her data with today's version is concerning and one major reason not to use it at all. You can check the recycle bin on onedrive.com for older files—it's possible some of the saves are there.
You can also search the computer for backups. If you want to go right to advanced search, click Windows key-R, enter cmd in the run box, and a Command Prompt window will open. Copy and paste this command in the window, and enter:
cd "C:\"
This says you want the next command to apply to the entire C drive. To search for saves, enter this:
dir /s "Slot_*"
The asterisk at the end means "anything can go here." If you find saves, copy (not move, for now) them to the correct Sims 4 folder and see whether they load.
You can search any other drive by starting with the same command: cd "X:\" , where X stands in for the drive letter. If there's an external drive involved, plug it in and double-check its drive letter.