[mothered]

Well, the item itself is on the boundary line of her property. It impacts land beyond her property though.

It's purely displaying a message, so there's no direct Impact (externally) when It's within the confines of her property. If people don't like It, simply look away.

I honestly dislike my neighbor's banner of his favorite football team (Real Madrid CF) on his back fence, but I can't force him to remove It so as with the above scenario, I choose to Ignore It.

It'd be like owning a sprinkler in your garden that drowns your neighbours flowerbed. Sure, the sprinkler itself itself is in their garden, but I suspect a legal argument can be made xD

I absolutely agree, for the fact that the sprinkler has a direct physical Impact on the neighbor's property, as opposed to being Isolated to Its owner's premises.