I wanted to add
It's a good idea to do all of her brushing on a table, it helps them learn to stand still when you need to cut their hair.
When I cut Lola's armpits I have her stand and I gently pull her leg forward and out a little bit so I can get under there and see what I'm doing. I don't cut the hair down to the skin because I'm afraid of cutting her.
This is a good link for cutting yorkie legs
Pet Grooming: The Good, The Bad, & The Furry: Scissoring a Yorkie