f KS and f KY means that was where her father was born. Although two different states were given, I'd say that the KS was a transcription error and that he was really b in KY.
Occasionally you'll find that the states listed that the parents were born in were totally wrong. That can be because of confusion, a neighbor giving the info, or something along the lines of when people ask me where I'm from, I say "California"- because that's where I grew up- but I was born in Germany.
1860 census, Madison, Sevier, Arkansas B F Jones 34KY Nancy Jones 36AL Elizabeth Jones 10 AR Willie P Jones 8AR Harrison Jones 5AR
1850 census, Madison, Sevier, AR
Benjamin Jones24KY Nancy17MS Frances2 mos AR
2 doors away John Jones58VA Mary L48NC Samuel W12AR Aron H10AR William8AR probably Ben's parents