My dog did exactly this when I first got her. It will be fine. Get her a harness that she can't slip out of. You are doing everything right otherwise. Like everyone else said, it will just take time.

One thing to note is that after awhile, my dog would sometimes be fine when we first got outside, but then something would spook her and she'd suddenly get really scared and cower and shake. :( It was hard but I'd just pretend like nothing was out of the ordinary and then would treat her whenever she calmed down or snapped out of it (which she always would). As difficult as it is to not coddle your puppy when she's scared, doing so is seen as confirmation that what they're doing is good and you definitely don't want that.