He has nothing to do with it spinning. He spins it in real life and it topples over, he spins it in a dream and it keeps on spinning. I dunno why you think that means he wants it to be a dream.
I agree that he uses her totem as a memento of her, but the totem works. If Cobb used Ariadne's or Arthur's totem they would work.
The point of a totem is that if, for example, Ariadne was the architect, she couldn't recreate Arthur's loaded dice because she's never felt its weight etc. As long as an architect doesn't touch your totem, it will work. The point of not letting anyone touch it is so it wont be touched by any potential architect.
Cobb's spinner will work even though it used to belong to Moll, especially since the only person who had touched it, Moll, is dead.
But they say earlier on in the film something like "Only you can fully work your Totem". Or something. Which means that because it isn't his Totem, it doesn't work properly. I can't describe it without the exact quote, but basically you can only properly use your Totem.