Consider SNOWY the server and SATCHEL the client. Make no changes to SNOWY, just run pconfig on SATCHEL to point to the mailboxes on SNOWY. Test the path to the \MAIL directory on SNOWY from SATCHEL using Windows Explorer to confirm you are using a valid path in pconfig. Make sure you have full control permission to \MAIL (including subfolders) from SATCHEL.
Alternatively, there is no need to run the Pegasus Mail installed on SATCHEL because you can share the installation that is on SNOWY. A shortcut to winpm-32.exe on SNOWY from SATCHEL is how you do it.
A few additional points:
1) You don't need your wife to exit Pegasus Mail when you want to use it. Pegasus Mail can handle being run by multiple users. It is the act of accessing the same mailbox simultaneously by multiple users that must be avoided.
2) There is an executable in the Pegasus Mail executables folder named wssetup.exe (stands for WorkStationSetup). Running this makes the registry entries and other system changes needed for a PC to run a Pegasus Mail installation that resides on another machine. You won't need to do this because you have already had Pegasus Mail installed on SATCHEL but this is important for anyone else considering doing this.
3) Be very careful when opening pmail.cfg with an editor. It is one of the few configuration files in Pegasus Mail that can be easily broken by manual editing. An inadvertant extra space or space deletion is all it takes.