Poor girl! Sounds like she needs some confidence building. I have to say, Jackson has come VERY far in 3 1/2 years. He was never THAT skittish in public, but was always a very shy guy. He'd shy away if someone tried to pet him, etc, and after did an agility class, his confidence really boosted. Another dog in the class used to be afraid of trash cans, etc, and the owners told me the class helped him out extremely. Also, we've always done trick training at home, and I have to say I just LOVE to see him at the top of his game. He always has felt super confident while doing tricks, and it's definitely boosted his self esteem... because it's, like, something he's like "I know how to do this!" and I can tell gets a kick out of people enjoying him.
I started by, of course, bringing him out to experience almost everything. He really began to love kids when I would take him to my cousins little league baseball games and I ALWAYS carry treats on me - I'd let the kids give him treats, and ask him to do tricks, etc. And just being around that, it really changed him.
Sometimes I forget what he used to be like, but then I remember... he's still very "aloof" with strangers - like, he doesn't necessarily seek out attention (aka he's no Lab or Golden), and he could do without, but he will voluntarily go up and sniff someone or let them pat his head, or if I say "go say hi" he will now... and I'm so proud of him! I've always encouraged him to try new things as well... if there's a big log? Jump on it! A puddle of water? Check it out! Tall grass... run through it! He's always been naturally curious, so it wasn't difficult, but I always encouraged it exploring and checking out new things. Even little things, like I taught him to leap onto my back, and to walk with his front feet on my feet, and with these kinds of things, he had to put a lot of trust in me, but it also builds his confidence.
I would bring "JACKPOT" treats (her favorite) with you when you see something that may scare her, and before she has time to REALLY be scared... shove a treat in her mouth, lol. Let her begin associating these scary things with something yummy. And I would just act like nothing is a big deal - don't react to her being scared, don't pick her up.
Kikopup on Youtube has some great videos about this kind of stuff.
Building confidence with surfaces - YouTube Kikos Kitchen Nightmares!- Training your dog to get over their fears clicker training - YouTube Barking Episode 4- Barking at Strangers- Dog training - YouTube