Can't say I've personally been to verify it, but the City Bus website for B7 has a map that shows where the bus should stop at Fanling Station.
Sheung Shui was easy enough, plus if I had missed the last minibus (or bus), at least it was a mere stop from Lo Wu. (not an MTR fan at all)
It's just a much bigger transit hub, so the options were nice (I guess it's at least five potential border crossings accesible from Sheung Shui)
(and for anyone trying Wen Jin Du or Sha Tou Jiao, those require buses to get past the border,
not HK city buses)