most definitely genetics 110%. stable dogs dont need to be socialized to be stable. they are born that way.
my friend has a golden that sounds like your pup. in training the trainer tried to come up to her and she cowered and hid under a chair. once she saw someone riding a bike and immediately took off running the other way and there was no way of calling her back. scared of random things like a football. submissive peeing. just skittish by nature. my friend has slowly worked with her and now shes ok and can go places and more confident but she'll never be what i'd consider a stable dog.
she will never be a confident stable dog but right now you need to train her so that she isnt fear aggressive. i had a pup that was barking at a plastic bag blowing in the wind. i thought it was cute. well it was weak nerves and he grew up to be fear aggressive which is time consuming and a money pit trying to fix it
btw its not your fault. you didnt mess her up.