Well, assuming she is telling the truth (which is a big assumption considering the circumstances, she could very well believe her story, but it may not be accurate) the dog was very likely just protecting its food source.
Dogs aren't humans, they don't reason things. The dog didn't consider the chance it was taking, and take action anyway for love of the owner. It was operating on instinct. It could have boiled down to needing the owner to open the front door or, like I said, it could have been to protect its food source.
Unfortunately, unconditional love doesn't exist in the animal kingdom. There are biological mechanisms in place to make a dog loyal to its owner, namely the pack mentality. Protect the leader to protect the pack.
I know, its depressing, innit?