Amazon has sticky cardboard traps specifically for pantry moths with a pheromone that attracts the little bastards.
I've used those too and they work well, but I think they're better at stopping a straggler moth from laying eggs--or for letting you know you have an infestation, because the trap is suddenly full.
If you can score some canning jars for her pantry food that will help a LOT.
This is what'll help more. Containers with lids are easier than packets to close, and
know you've closed, than zip-top bags. If her vision is poor, she can still tell she screwed or snapped a lid on and doesn't have to go back and feel the bag.
Get her a set of, say, those
OXO Pop storage containers as a gift. Even if you don't have bug problems, a set of storage containers is a nice gift if you're a mom-type person.
Every week or two I am there I source the issue, remove it, then they find a new spot by the next week.
This really sounds like they have a hiding place you haven't found yet. I don't think it's crumbs; I bet there's a rogue box of noodles hidden somewhere, or you guys clean up everything infested but you miss something with eggs but no moths yet. By the time you're back, they've spread again.
I hate pantry moths too, so much. Whenever I've had to get rid of them, I go through and open everything and throw out what needs throwing out--then put everything that
looks fine in a container, or at least put a zip-top storage bag around it. A week later, a box of Rice-a-Roni that looked OK will be inside a zip-top bag full of moths, but at least they didn't spread and start the cycle over again.
I also ended up spraying barrier insecticide in all the nooks and crannies like the space between the edge of the shelf and the back wall of the pantry, the cockroach stuff that's supposed to last for months and months. The cockroach spray is probably the most effective thing I've done, tbh, but there is a potential contamination issue that comes with it.
I'm a big fan of diatomaceous earth for applications like this. It's not invisible like barrier spray, but it's less worrisome for being around food.