@Martin Slack
Then I can create a backup on my PC on an external drive, plug the external drive into Theresa's PC, and restore the backup (first time).
Yes.
Then after that, on a regular basis, I can convert the catalogue.
No...
There is nothing to convert, you'll be in the same PSE version.
So, if you don't want to repeat the whole process (backup on external drive and restore on the other computer) my suggestion is to:
- backup to an external drive from your PC
- restore to (preferably another) external drive.
Then you use the external drive alternatively by plugging it in either PC.
The external drive will hold your shared library, no need for backups/restores afterward.
Of course, you are free to also do a backup and restore from the external drive to either of the PCs when you have time and if you have enough disk space.
My remark about different catalogs is a general one for people sharing the same computer. You may wish to have a common library (file folder tree) and manage it differently. But what is done in a catalog is ignored by the other. If you use the same external drive, you'll share the same catalog, but you may want to create a different one as a subset for example. Not your original question, sorry if I have made it confusing.