well if the vcu is intact and just the rear prop removed from splines its guaranteed to have been removed for a few reasons...vcu is siezed, diff is wound up and noisy when prop connected due to sized vcu putting extra strain into it...or indeed the ird may be noisy ith the extra load on it when the diff is connected via the rear diff.
Either way it looks expensive, not easy to check vcu without rear prop on..
suppose you could whack it in first gear and stick some stilsons on the vcu output shaft to see if it will move at all but you aint gonna gain a lot from this crude method - and you'll probably shear the splined teeth orf anorl.
She's either gonna have to get a new vcu and then repair the diff or ird (or both if they are gone (diff approx £500, IRD approx £900...all plus fitting) and she will need a new rear prop section too - and vcu bearings.
If she is lucky then its just the vcu and rear prop she needs ..prob approx £400 worth if she knows someone who will fit them for her.
Bottom line - never buy a 4x4 with half the drivetrain missing, her horses arent gonna be getting a day out in the near future :O)
