Perhaps you should look for a physiological reason and explore some possible causes of dehydration before jumping on a new regulator to cure her problem.
I think you should be sure that she is well hydrated and has some dive experience, if she is in the 0-24 dive bracket as you, before you spend money on new regulators.
As you gain experience and get used to breathing tank air and if you stay properly hydrated the dry mouth problems should dissipate. Also if she is taking antihistamines or a host of other medications this may create dry mouth problems.
Hydration means drinking water along with drinks containing electrolytes to help replenish salts in the body. Soft drinks and diuretics like coffee and alcohol or things with sugar like gum etc. will make it harder to stay hydrated during periods of higher diving activities. Hydration begins well before your day of diving.
Look through the DAN website and do some more reading on the subject, it can't hurt and may save you some change while helping your wife to be more comfortable.
I dive an Aqualung Legend and have never experienced dry mouth, so naturally I am less inclined to think it is equipment related and more to agree with WVDiver. Also, I am wondering if the mouthpiece may be a factor, did a comfo-bite come with your reg setup? I have tried a few mouthpieces and found that made a profound difference, so you many want to experiment with that (cheaper) before buying a new reg.
Donna