I am so very sorry for the loss of your Golden. How old is Sadie about one year? And your new Golden puppy is how old?
It is difficult to give advice without seeing the dogs interact, I do have a comment, and that is to be (which I am sure that you are), very present when you allow the two to interact. And do be ready to intervene.
I am a large dog owner (with a BRT puppy who is currently 9 months old and about 75lbs or so), and my concern is for your Yorkie not getting injured. Quite frankly I correct my Yorkies aggression to my large dogs, every single time that it is warranted. Why? Because he needs to know he can't act that way out and about with strange large dogs. Unfortunately and I am only supposing this, the size differential is so huge my biggies felt no need to discipline him when he was a puppy and acting out.
Even now they don't discipline him. But one swipe of a large paw could break a leg or a back
I am just wondering what is the spray bottle to be used for? And when and how?
I also do not walk by myself a large and a small dog together.
I know this might seem like a bit of an overkill, but all you need is one bad experience and hopefully you learn a lesson with no-one getting injured.
I do not allow my Yorkie out free in our backyard with our puppy BRT. She has a bit of a prey drive, and the chase is quite frankly dangerous to Razzle our Yorkie.
BAll games etc, are done either one on one, or the two Blackies together. It is only in swimming will all three be out together in the water, and that is only if hubby is with me.
I am sorry for the ramble afield as it were. Dog aggression is not an easy behaviour to deal with.
If your Yorkie is afaird of the trainer, I do wonder why? Has Sadie been well socialized to strange ppl and dogs? If yes, then doubly I would wonder why Sadie is afaird of the trainer.