It's not that uncommon for a new part to be faulty. The valve was probably sticky, nothing to do electrically, I think the service manual would have said to twist the valve (removed) in your hand and listen/feel it swing side to side to make sure it isn't sticky. That being said, if it's only a bit sticky then you probably would have needed some experience or a good valve to compare.
I think you are right, there was probably more to it like a vacuum leak and or something not assembled correctly but probably no parts were needed.
Good that she's fixed though! and your ego should remain intact
re: the sticky is why I asked if you used carb cleaner on the valve, I think you know but, for others that don't, carb cleaner will swell/ruin the o-ring seals in the IAC motor or throttle body and create exactly the problem you had.