I'm not sure how helpful my answer will be to you, but I will post anyway in the hopes that it may be.
I'd be very concerned about poo encrusting a pig's feet, if the issue is as persistent and serious as you describe. Even a micro cut on one foot can be the entry point for foecal bacteria, and then you may end up having to deal with a serious infection and/or pododermatitis. Plus, the more her nails grow in an abnormal shape, (possibly) the more uncomfortable walking will be for Cinnamon. So she will soiling her feet and not moving away.
My only suggestion is to check, possibly with another vet, the reasons why she isn't so active and also to try to find the root cause for the gut problems. A foecal float test can determine the presence of parasites, and then with a foecal culture, your vet can check what is the exact bacterial composition of her stool and if there is a proliferation of one type of bacteria, and also whether there are viruses or fungus. Microscopic examination of the stool can also be helpful for the same thing. In that way, you can target the exact cause for her gut issues, rather than just shooting in the dark.
Aside from this, you can try to stabilize the gut with probiotics and bio-sponge, which is at least readily available "across the pond".
I'm sure you are already doing some or even all of the things I suggested, and I'm sorry if my post is redundant. I just wanted to say from personal experience that it's very satisfying to treat a pig after a correct diagnosis, because we can than use the appropriate medication and the pig seems to improve overnight.