My grand dog is misbehaving

I was over to let them out and sat with them for awhile. I was sitting in the dining area, and heard a noise in the kitchen, just on the other side of the counter. The big dog was trying to pull the trash can out from under the sink. In the past, she'd very rarely open the cupboard under the sink, pull the can out and and tear up the trash. Now she is doing it so often, they move the can to the garage or bathroom, so she can't get to it. They've had a little dog for a year, and since her spay last spring, she's gotten a little chubby, so they put her on a diet, cutting out canned food and changing her kibble to another brand.

Before they cut out the wet food, they gave the little dog a spoonful of canned food, and they would also give the big dog a spoonful. Until they got the little dog, they gave the big dog only dry food.

I think the big dog is tearing into the trash because she misses the canned food. I can't think of anything else that changed.

Any thoughts?