My dog complains when we have a new bag of dog biscuit but still give her stale biscuit from the open bag.

No need to No True Doberman the discussion. There are plenty of picky dogs in the world.

Some dogs (like people) are more particular about their food. Your pet might be bored with their current diet or may have developed an aversion to the way their food tastes, looks, or feels. Additionally, dogs receiving frequent treats or table scraps may become reluctant to eat their regular dog food, in the hopes that a better-tasting treat will be coming along shortly.

https://www.greatpetcare.com/dog-behavior/reasons-your-dog-is-a-picky-eater/