another approach is to work with playlists.
We use the Java stand alone client as player and with that tool you can easily create playlists for you and your wife. Those playlists sit in the sqlite database, which as well holds all the music information of firefly.
If you use itunes as client, you can see and use those playlists as well (but you cannot create them with itunes).
We have a collection of about 10.000 songs; no problem for the slug.