How about this song by Alison Krauss & Union Station?
Alison Krauss and Union Station - Baby, Now That I've Found You [Music Video] - YouTube
She has a lovely voice and sings in a country style, so it might be worth looking through some of their other tracks as well.
Or how about this acoustic-style cover of Wild Horses by The Sundays?
The Sundays - Wild Horses - YouTube
Ingrid Michaelson has a couple of songs that might be appropriate:
INGRID MICHAELSON - "The Way I Am" - (official music video) - YouTube
Ingrid Michaelson - Everybody - YouTube
This song points out how love can make even a bad day seem awesome.
Dido - Thank You - YouTube
Whilst I hate to recommend Taylor Swift, this duet of hers with Ed Sheeran, is a country-flavoured love song, with male and female singing.
Taylor Swift - Everything Has Changed ft. Ed Sheeran - YouTube