[BostonRott]

If she knows how to heel, and she gives you "lip" again, I'd put her into "boot camp heeling." I.e. dog screws up, you give a firm verbal correction, and then immediately start making the dog work briskly and with purpose. This will get the message across to the dog "I am the leader, you listen to me."

What were the specific circumstances when she growled? Did you lean over her? Did she have a favorite toy? Was she near a food bowl?

Sounds like you're doing things well. I personally am not a fan of "in home" training for Rottweilers, and I think you'd be better off setting up a private lesson with the person who is teaching your group lessons. this person has already seen you and Gypsy in class, is familiar with your issues, your relationship, etc.