I think your analysis is correct.
It sounds like the 3rd filer (2nd daughter) either reused the 2nd filer's (1st daughter) file or perhaps she saved her file in a different folder.
Unless, someone did backups between these actions, the first file would be gone.
NOTE: Turbotax usually creates saved files in the same folder. It us usually under or in the folder named Turbotax. It is possible that one of the files is saved in a different folder. To check this, you can search your entire pc for a ".tax2021" file. If the file is elsewhere, this will find it.
I suggest a warning to both daughters for next year to avoid this. I also suggest when a return is completed, save a PDF of all the forms, worksheets and data on your computer.
