but everytime he comes over, he'll grab her by the scruff of the neck, until she cries out.
For starters, anyone coming in and grabbing Lady like that would be out the door so quickly their head would be spinning.

That isn't helping the poor pup at all. there should be ONE person handling discipline. Additional people, especially someone who isn't there all the time, trying to "help" is just going to confuse her.

What you have been describing is normal behavior for a puppy. Zoe looks like she has lab in her, and labs have a LONG puppyhood.