Generally it is a submissive behavior; we can assume this as long as her vaginitis is indeed under control.
Rather than let people approach and fawn all over her (which is likely opening the flood gates), have people ignore her and let her approach them. They can hold pieces of treats and let Zoey come to them and take them from their hands. i.e. people are Pez dispensers.
This will help Zoey gain confidence. In addition, do not allow people to lean OVER her or pet the top of her head, but rather they should allow her to do the greeting and they should be rather happy, but not in the pup's face. They should ALWAYS pet the pup from underneath the chin.
See if this helps.
Some dogs are softer in nature than others, and it's our responsibility to encourage confidence in our pups. What she learns now, she will use later.
Submissiveness, just like dominance is not a black and white thing. Learn your puppy's body language.
That your trainer has not addressed this properly concerns me a bit.