Welcome to YT!
Isabella sounds like a little imp..."shy" and timid, but not around other yorkies. Every single dog that I have had the opportunity to share time with over many years had their own unique quirks and personalities. It is so much fun to be able to learn about them, and to have special, unique interactions with each one. I hope that Isabella grows more self confident around others soon. I am sure that your exposing her to new experiences, opportunities and personalities in a non-pressure setting will help.