If you already working on a catalog, you can build smart previews for the catalog as well:
- Select all the files , and then click Library > Previews > Build Smart Previews.
Smart Previews are stored in the [Catalog Name] Smart Previews.lrdata file, located in the same folder as the catalog.
While transferring the date to the editor you need to transfer the following files:
Lightroom Catalog Previews.lrdata(Normal previews)
Lightroom Catalog SmartPreviews.lrdata(Smart Previews)
What you need to do is select the photos in your catalogue and then run File > Export as Catalog. Tick the option "Build / Include Smart Previews". This generates a folder containing a catalogue and smart previews.
Send this folder to your editor, and ask him to send back the catalogue (lrcat file) afterwards.
Then use File > Import from Another Catalogue to bring his edits back into your catalogue.