Does my dog know she's not getting as much as our other dog?

I don’t think a dog looking at a pork chop is aware of anything in the world except that pork chop.

Our experience over many years is that dogs don’t judge the size of the treat, just how many times you hand it out. You could give Dakota pieces two or three times as large, as long as Duchess gets as many handouts as Dakota gets.

^^^ Yep!

Oscar isn’t big enough yet to be able to eat an entire can of cat food, so when I’m passing out the stinky stuff, half goes to Oscar, and half goes to Russell (my dog).

Russell, of course, can eat a half a can of cat food in no time flat. This results in him staring longingly at Oscar eating his half-can, and I just know he’s jealous.

He’s obviously not smart enough to judge that they both had the same amount, but he definitely knows that he had 1 minute worth of food, and Oscar has a half-hour worth of food, and he’s not pleased that he does not also have a half-hour worth.

No.

Dogs may not have that level of understanding, but there are other animals that do. This is a classic video showing that capuchin monkeys know the difference.