I wouldn't push your mom all that much - I feed Nutro senior dry, and add a bit of wet food morning and night. If her cats are eating happily, are a good weight, poo and pee fine, and their check-ups are top notch (and I bet your mom gets blood work done) are good, well.....
There's probably not a food out there that hasn't had quality control issues (and I'm including human food in there).
Nutro has been very upfront about quality control issues, and have self-initiated recalls (unlike, apparently, Evangers and Natural Balance, both of which are apparently having some issues right now). You can check on the Nutro web site regarding the particular lines and dates that were recently recalled, by Nutro themselves. Evanger and the food it produces for other private label companies are definitely being produced under hazardous conditions right now - and at least as of last night, Evanger hasn't owned up to it on its web site. They've had issues for quite some time now, but apparently haven't made any efforts to correct the issue (unlike some of majors after the Menu food recalls - up to and including buying their own plants to manufacturer wet foods). I personally suspect Evanger tried to ramp up production too fast post-Menu recall - to take advantage of the demand for 'holistic' food and because some buyers just don't trust a larger company, whether for good reasons or for bad.
I truly don't think there's one food out there that hasn't had issues some time or another - including those that claim to have never had a problem. After all, recalls in the food industry (human or pet) are almost always up to the manufacturer - and some companies are better about 'owning up'. So, just because your vendor says they haven't had any problems, doesn't make it so, sad to say. Evangers now has been hit by the FDA - a nice big red flag, to me.
One thing about Nutro is that they follow the animal feeding test protocols used by AAFCO - a lot of the smaller companies simply formulate their foods against written formulations. You pay your money, you take your choice.
Basically, if your mom's cats enjoy the food, are healthy, and are getting regular checks by a trusted health care professional who's happy with their health, I wouldn't be too paranoid. And mom can always get her cats a water fountain to increase their water intake -or maybe get one as a present?