Our mix was a sweetheart to humans (for 99% of her life), but occasionally lashed out at two of our other four dogs who overlapped with her in our household. She was indifferent to the other two.
We had things managed pretty well for several years, but when she started getting older, about ten, she started getting confused, and forgetting to eat, and losing a lot of weight, and getting grumpier and making terrible decisions. When it spread to humans (she bit my hand twice in two days), we knew her time was up, but we gave her a send off in accordance with her being a good girl, as they all are.