We have to give our dog valium before we take her in to get her nails trimmed. She is quite delicate when it comes to anyone touching her paws.
Start by just turning it on and giving her a treat.
Start with just ONE nail at a time. I started with the front dewclaw (on my dog that still has them). I just touched the Dremel to the claw, then gave a treat and shut down for the day. It took days, but now my dog just sits there while I grind down her nails.
The Dremel is better than the scissor-type clippers because it doesn't crush the nail, which hurts the quick.