It worked!!!! I bought a tiny Kong toy and put a little peanut butter in it and let her put her head through the harness to get to it. She was totally fine with the harness!!! Y'all are amazing.
I think the harness is too big, though. I bought the extra-small, but I think I'll need an extra-extra small.
Thank you to everyone for your advice!
I can't wait to walk her.
(She has had her Parvo shot)