Actually, if youre doing 8 to 14 miles a day in hilly Virginia country, Id call you serious day hikers.
But because your wife seems to be having this problem, and you are not, its pretty obvious that her boots dont fit. Theyre a bit too short, and maybe too wide as well.
Does that mean you need to buy new boots? Not necessarily. For starters, take them to a good shoemaker in your area (yeah, shoemakers arent everywhere, but you ought to be able to find one) and have the toes stretched out a little. That might do the trick. If it doesnt, then the next step might be to swap out the stock insole so that the foot doesnt slide forward so much. Superfeet (superfeet.com) makes a high-volume" insole for $35. It provides more cushioning and support than most stock insoles, and it also soaks up some interior space for boots that are loose or too large.
If THAT doesnt work, then its time to buy new boots. I dont know what she is wearing now, but its possible that the boots werent built on a womens last. If they werent, then the boots are not going to fit her heel or arch as well as those built specifically for women. Asolos Stynger GTX ($165; asolo.com) are excellent mid-weight hikers that are fine for day-hiking but have enough heft so that a downhill stretch wont torque them out of shape. Same for the Montrail Torre GTX (also $160; montrail.com). Moreover, Montrails boots have a uniformly good fit on a wide swath of the population. Lastly, Scarpas Mustang ($168l; scarpa.com) is a top-notch new boot from one of the best makers out there.
All three boots have a Gore-Tex liner for a little extra water-proofing. And their leather uppers give good foot protection.
Hope that helps!