Cardiac concerns is something I have much experience with unfortunately. Like your vet said, I wouldn't be too concerned over a 2-3 rating. My old dog stayed at that rating for about 3 years before it suddenly progressed to a 5. At the time, I unfortunatley didn't know about the option of natural supplements, so it's not something that I ever looked into.
However we did start giving him Vetmedin. It was a low dose in the beginning (I believe just 1 pill every other day).
Years later when he got really sick and we brought in an emergency canine cardiac specialiest, he said that the Vetmedin was probably what had saved his life and kept him so active for so long. I guess we'll never know for sure, but it was comforting to hear that we had done the right thing.
When it comes to something like this, there are so many options available. Depending on the type of heart disease that eventually prograsses, an echocardiogram may or may not be helpful (in our case, the vet said it wouldn't be worth the cost because it would provide such limited information).
My point is, I know how scary it is to learn that the murmer is progressing. But just remember that it took a few years to get that far, it may take a few more years to get any farther. And when it does, there are many treatment options, medications, and cardiac specialists there to help.
Like your vet said, keep an eye out for coughing, or getting winded more quickly after excercise. Also, it's good to start taking her pulse on a regular basis. When she's at the vet, it's probably elevated due to stress. But when she's relaxed at home, you'll be able to tell what her true resting heart rate is. If you notice it increasing over time, than that's another sign that heart is having to work harder than it used to, to pump blood.
Timber - Siberian Husky - 3 yrs old
Jasper - Siberian Husky - 3 yrs old