how to recover subfolders from a backup?

My wife had a ransom ware virus (20 Nov): I re-installed Win Home Premium and eM Client 7 then imported her emails from an export to .csv file (eM Client 6) a week ago (we spent time & money trying to get rid of the ransom ware). Unfortunately I assumed that she did not have any subfolders so I now need to recover them. Fortunately, I did also did a backup (20 Nov) so could load that but would ii prepend to her current emails?   If not, would: forward (in case of any attachments) all required emails post 20 Nov to herself, restore from 20 Nov backup then receive all emails be a feasible solution?

WRT recovering eMails from previousy exported file (on memory stick): it prepends/appends/merges - so no probs.