The Library Radio is essentially a mix of a subset of tracks from the library including a few factors:
- How popular the track is (last.fm rating).
- How you’ve rated the track.
- How recently you’ve listened to the track.
So it’s likely not going to work super well for collections where two people have “competing” styles in a single library.
Something your girlfriend could do is just make a smart playlist based on highly rated tracks, and shuffle that.