HOW DO PEOPLE HAVE SO MUCH MONEY???

I'm nearly 30 and I still simply can't fathom how much money people have.

It seems to me that it's still possible for Morton himself to have removed the cufflinks and hidden them in the valet's sock drawer in hopes of reclaiming them and collecting the insurance money. There's a gap in time between when the two friends left, and Gene's location at that time is not specified. It's also possible that Morton took the dog out as a cover, tied it up outside and sneaked back to move the cufflinks. We don't know how far away Archie was parked, how long he tried to start his car, and whether Morton had time to go inside and draw his friend's attention to the terrace before sneaking out again. I wouldn't rule out Morton as a suspect based on the narrative given above.

You've got to hand it to her. That is one hell of an industrious child.