Hi
I have in the past had a dog (when I still had bigger dogs) who unlike his siblings suffered from nail splitting condition, the vets tried many different drugs and supplements but nothing really worked. I gave up with the vets after a while and started trying to treat it myself for the most part, only going back to the vets to have a nail fragment removed. I found after many trials of different things that omega oils help to stop them splitting as badly. But as you know once they start to crack it can be hard to stop the crack spreading. I ended up putting him in padded boots like the dogs that do search and rescue wear. This at least stopped him catching them once he had stopped walking funny and trying to rip them off. Then I tried to keep the nails as short as possible by weekly trimming but before trimming I would make him stand in the bath with a couple of inches of water to soften the nails so that when I cut them they didnt splinter as much. Also make sure you get a really sharp pair of nail clippers otherwise trimming will just crack them more. I know it sounds like a human beauty routine but it did work and he went for many months at a time not needing to wear the boots by this trimming method.
Read this link about all the possible conditions that you still need to check he hasnt got first as their may be a vet treatment for them-
http://lowchensaustralia.com/grooming/nailconditions.htmYou may also want to consider switching her to a complete food like royal canin or pro plan that have ones for coat condition, these have the same omega oils in them.
Good luck
Emma