I'm a little confused here, you say she foundered 4-5 years ago, has she had any episodes since then do you think? It is quite possible btw that she *has* and you have not noticed... a mild bout of laminitis is not always enormously dramatic, even if you have done a good job of reading up on what signs to watch for and are paying close attention.
If it was just one bout of laminitis, years ago, with no rotation (which btw would technically make it just laminitis, not founder per se), it should not be having much of any effect on her feet now. If it was just that once, any feet problems she has now are almost certainly something else. If there's been no recent laminitis and she is actually sore, not just having her hooves chip up, then you NEED to have her evaluated again by a vet.
OTOH if she has had more episodes of laminitis since then, a) I hope she is being managed as a chronically laminitic horse i.e. NO GRAZING AT ALL FOR HER, give her a dirt or sand lot and feed hay on a matted area. And b) you will just have to find another good farrier to work with you, ask your vet for recommendations, etcetera. There is just no alternative to getting a good farrier coming out there.
FWIW, crumbly hooves are sometimes just inherent to the horse. Feeding a good hoof supplement with biotin, methionine and zinc in it often helps. There's no evidence I know of that other ingredients necessarily do any good, and you will have to look up what the minimum #mg of biotin per day you need to be feeding. Do NOT just go by the dosing instructions on the bucket of supplement, some give an unnecesssarily high recommendation to get you to buy more, and some give an unhelpfully low recommendation to make you think they're more economical. Another contributor to shelly crumbly hooves is sometimes a diet too low in protein. She may need more higher-protein hay, e.g. very good grass hay instead of more-mature grass hay, or an alfalfa mix instead of straight grass hay. If she has had more than the one bout of laminitis she should probably not be getting grain, but if she *is* getting grain (or pellets, whatever) you might consider moving to one with a higher % protein.
(edited to add: another contributor to cracking breaking hooves is frequent wet/dry changes in her environment. Does she by any chance go out in a muddy paddock? If so, anything you can do to correct the problem so that she is never standing in mud will also help her hooves).
Hope this helps, good luck,
Pat