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I am sorry you had to wait so long to get a response, different experts are online at different times and each of use has different expertise.
I noticed that no one has yet answered your question and I have a suggestion. There is nothing that I can think of that you could give that is over the counter but you may want to talk to your vet about having a sedative on hand to give her for nail trimming time. Another thing that may make things better might be to use a dremmel or sander took to file the hooves down instead of using trimmers. This technique works well with dogs that are averse to the pressure that nail trimmers causes. You have to acclimate them to the sound of the dremmel and the feeling of the vibration so it needs to be done slowly at first but once they are used to it they seem to tolerate this much better than the other methods.
The cracking of the hooves is a different issue and may or may not need to be addressed separately. Yes they can crack if they are too long, however I would be concerned about the integrity of the hooves in general if they are cracking and she may need to be supplemented to help strengthen the hooves.
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