I always have a harness on Jaden and once Jewelina's shots are all done and she can walk outside she will have a harness too. They are both very obedient and will follow me but I am just too afraid to let them walk without it. You never know what could happen, they could see something and decide to go off chasing it. You'd be suprised how fast they can be!
Or perhaps they get scarred and dart off into the road....
Or maybe a big dog will come out of no where and come to attack them..you wouldn't be able to quickly pick her up because most likely she would be afraid and start running away, and a larger dog could easily catch a yorkie...
I live by the motto "rather be safe than sorry". I know I could never forgive myself if something happened to one of my babies because I didn't do something so simple as clipping on a leash.
If I were you I would absolutely have her on a harness or in a shirt/sweater with a D ring on it so you could clip a leash on there.