If it's theoretically the right price and she's not even getting any viewers then either she has terrible estate agents or there is something about the details putting people off (which would also argue for terrible estate agents, to be honest, because they ought to Know That Sort Of Thing).
The gravel garden (and pond) would definitely put me off. And really, how many nice elderly couples are shopping for four-bedroom houses? And how many parents with young children want to completely re-do the garden immediately after moving in? I think there's a good chance that if she really wants to sell then redoing the garden in more family-friendly style (and maybe then putting up the asking price by the amount that she's spent on doing the garden) would be a worthwhile investment.
Other thoughts... Is that the new kitchen in the photograph? It doesn't look new IYSWIM, it looks a bit poky and dark (and I'm not sure that the tile pattern is helping). I read the description "having been recently re-fitted with an extensive range of wall and base units with spotlights under untis and pelmets, display unit, work surfaces, wall mounted Belling double oven with twin grills, inset Stoves gas hob, stainless steel twin sink and drainer, space for upright freezer, fridge, washing machine or dishwasher, extractor fan, floor level kick-strip located fan heater, fully tiled to walls, enclosed balanced flue gas boiler, double glazed window to rear garden, door to rear garden." and then look at the picture and think "Oh." If it looks good in real life maybe get the photo taken out of the details so that people don't get too many preconceptions?
In the lounge my attention was immediately drawn by the red carpet (and the border/wallpaper looks a bit dated). I'd be inclined to paint the walls and put down something more neutral/seagrassy if I were house doctoring. And move the furniture away from the walls. And Ann Maurice would definitely put a huge great mirror over the fireplace
The only other thing that would put me off is that it's a 4-bedroom house with only one bathroom (plus a downstairs shower/utility room). Admittedly there's not much she can do about that, although if there's any possibility from a practical point of view of, say, converting a corner of the master bedroom into an ensuite then just saying as much in the details might help? (I suspect that actually doing it wouldn't give great return on investment, although the estate agents might have a view on that).