She's gotten him this large, three pronged, hallow chew toy that you can put treats inside of, with one of the knobs being a squeaker. So now all he does is roll the toy over and sniff around for the treat. He completely ignores the squeaker, which used to be his favorite thing.
So basically this puppy is pulling the one armed bandit and hoping for a payout. Is there a help line for k9's?
There was a scientific study with rats in a similar setting. They got addicted and overate when there was a treat sometimes, but not when there always was one. That's also how slot machines work.