Welcome to YT!
You said it's a retractable leash? So it has a heavy handle, right?
Generally, you get puppies comfortable with their harnesses and leashes by putting them on and letting them drag them around the house. You do this several weeks before actually taking them outside.
Now, you probably can't have her drag around a retractable leash. Do you have a short nylon one you can substitute for now? She may also feel less intimidated by that one.
Just go slow, and you can always use treats.
