Happy is always desirable, because it boosts rather than overrides the dominant emotion. I'm not sure why a happy buff would stop a sim from being inspired. If you have other inspire aura items, the auras are turned on, and you done something to get inspired and are still getting overridden by happy, something is definitely bugged. Most aura items need to be manually activated. There are a few exceptions but almost all of the inspired one have to be. Maybe don't use the sink? There are enough other inspire buff items that not using that one is no great loss, especially if it's causing issues.