Sydney( not my Yorkie) was a
very hyper dog from day one ! I'm not sure if she was nervous , she didn't appear nervous to me ...just
VERY hyper .There were no other pets in the house at the time though , so I'm sure that cut down on any would be nervousness or aggression.
I thought I was going to have an aggressive doogie based on her play with us . Many a times I wondered "What the heck did I get myself into?"
I started at the suggestion of my vet "letting her know her place". I guess that is the same as NILIF . She told me Sydney had to sit and wait to eat , to go out , for a pet etc. She just needed to know her place in the line ( or in the pack I guess) It took a while but does work. It is also much safer because the couple of times she did get away from us she would not stop no matter what , and it's safer for us because we had to chase her.
She also said she needed lots of exercise and maybe agility training or something similar because she was most likely bored and needed her mind focused on something positive to do instead of negative aggressive play. So lot's of walks/runs and a obstacle course helped.
As for the whistle anything that gets her attention would be good. Sydney never seemed to hear my voice say no. I would use a clap and a loud naaah , I wish I would have thought of a whistle.