The first thing you both should read is this:
Groundwork to Becoming a Pack Leader
This method really made a difference when I adopted a very high-strung lab at 9 mo. old who had no training or pack structure in her previous home. Man, she was quite a pill at first, but after going through groundwork, she knew who was in charge, and the respect level went way up. You need to start this now, so you can have the dog ready to focus to her when Basic Obedience starts.
As far as you being involved in the training here's a quote from the Pack leader article:
"THE FAMILY PETTING AND PLAYING WITH THE NEW DOG
This may fly in the face of people who want a family dog but the fact is in the beginning I never allow family members to pet or play with a new dog.
My primary goal is to establish a family pack. I can best do this by firmly inserting myself as PACK LEADER. once that is accomplished I can easily step in to help establish the rank of other family members within the pack."
So, your GF needs to be the only one really making any contact with the dog at first to avoid confusion about who is the Pack Leader here. I am almost sure that I have either read or heard Ed mention that the training is done by one person, in this case your GF because two people have a hard time being consistant in the training. But I think you understand that, and are asking how can you tell her to do it right without upsetting her.
When I started groundwork, I made my GF not look at her, no touching, nothing. This would apply to you in this situation. Also, anyone who comes over, same rules. This really upset my girlfriend, who wanted to play with the dog, and such, but the bottom line is, if I didn't follow pack rules, the dog would be confused, and I wouldn't have the focus on me, which allows me to control the dog. She knows now that I am the pack leader, and through
me she gets pleasure, not anyone else.
You want to help her with training, but don't want to take over. Well,
she is the one who should take over. It is her dog, after all. This dog will be alive ten years from now; will you all still be together then? Who knows? But her and the dog sure will be, and she should want to make the most of this long-lasting relationship by being a leader for the dog. If that is not in her personality, trust me, dog training will certainly bring it out of her!
When you get the Basic OB DVD, you will learn about marker training. This is one of the most fun things I have done in my life! I think she is really going to enjoy it! After she puts the dog through groundwork, and starts with the basic obedience for a few weeks, update us on how things are going. I am confident that she will have new character traits like leadership that she never knew was in there! Good luck...