Um, no one's mentioned exfoliating sole?? It is natural for old, dead sole to become 'chalky' and loose, if for some reason it hasn't exfoliated. This may be what your friend is seeing. Without more info, don't have much to go on.
If the horse is on wet footing & her feet need help in drying out, soaking in a strong saline solution can be helpful, drawing out excess moisture through osmosis. I would not be putting any other topicals on them, aside from if treating infection, and would avoid harsh chemicals such as turps, acetone, keratex, etc. It doesn't generally help soles to become harder anyway - what is needed is for them to *grow* thicker. Therefore, diet & nutrition is one of the important factors.
Regarding the senior feed(and most manufactured horse feeds), if it's grain/starch &/or sugar rich, it's not generally good for horses and founder(not 'like founder') is one potential effect of that sort of diet. Just going on flakey soles is no reason to suspect laminitis tho.
suddenly had to have shoes put on a few weeks ago because she was getting rocks so far stuck up in her sole that they were causing her to bleed...
If the horse has got extremely thin &/or soles that it's actually causing bleeding(where were the rocks getting stuck?), then I'd suspect lami &/or other issues & get your friend to find a very good horse vet & good farrier & perhaps get xrays too. Shoes IMO won't help that. As there are differences of opinion wherever you look, among 'experts' & otherwise, I also suggest that one of the most important things your friend can do for her horse is to educate herself as best she can, so she can make some objective choices about how to manage her horse.