any suggestions on how to help my new dog to be more social and not fearful?

give her trits (like my dog)

At four months old, she is still young and it's normal for puppies to be easily scared. The fact that she's not used to being around humans obviously doesn't help, but that does suggest that's why she is so fearful. So at least you (probably) know the source of her fear.

The important thing is to make sure she knows she can trust humans. Make sure you spend as much time as possible with her, and be very gentle and kind. It's also a good idea to assure she gets used to being around a variety of people, so any dog-loving friends and family you have should interact with her too. Again, just make sure they are all gentle with her.

I've had pets who have been afraid of sudden sounds and movement before, and they seem to overcome their fears naturally the more confident they get around humans. I also think it may come with age. Obviously, you can't always stop sounds and movement from happening, and so it really is something your dog needs to get used to.

I suggest you focus on spending lots of time with her and letting her know she can trust you. I expect she'll get much braver and more playful over time as long as you give her love and attention. If for any reason she's still getting nervous around loud sounds and sudden movement after a few more months, I don't know if that's something a vet can help you with (they may know of some psychological cure - I really don't know, personally!). To avoid more trauma if your dog is really scared, it's best if you call a vet to come to your home instead of taking the dog there.

Good luck with everything, I really hope this will help you in some way! :)