If the refusal to eat happens only with a new bag, it is likely your dog is sensing something about the food, not just bored with it. You are lucky the dog is this sensitive. .
This is what I am suspecting. She only refused once I opened the new bag. Before that, she had been eating that same flavor as fast as she could swallow it. What concerns me is that this is the 2nd bag she has refused in three months. I brought home another new bag after the refusal, and she tore into it like she hadn't eaten in days. It's definitely NOT her being finicky, she is not a picky eater by any means.