I've had a similar problem with an Imaginary Friend. After moving to a new house, my child's IF disappeared. The strange thing is that there was a little girl standing at the edge of my lot, on the sidewalk. When I hovered my mouse over her, she had the same name as the IF and had the same portrait that was in the relationship panel. For me, the portrait would randomly switch between toy form and human form. She never moved, and I never tried interacting with her for fear of it messing up my game.
I'm not sure about the items your sims received, though. I know when sims get married (I don't know if this is from Generations or the Generations patch) their friends might send them wedding gifts. Maybe you checked their mail and just didn't notice it until later? I'm not sure if that would be it though because the gifts always go to the family inventory in my experience.
Not sure if these will help any, but you're not alone in a disappearing IF.