Wanted: XS or S mountain bike

My niece is looking at kicking off on this thing called mountain biking.
Anyone have or know someone who has a decent small or extra small mountain bike they no longer require that doesn't need new everything? Definitiely needs to have fornt suspension, not to fussed on what type it is. Disc brakes would be good too! Doesn't absolutely need to be a ladies bike if it's the right size etc.