Yeah, I don't think there are any "shoulds" about how much we love our GC either. Everybody is different.
I must admit, I did feel that rush of tenderness for each of my grands that I felt for my newborn DDs. But that's probably cuz I was invited to the births and each time, got to hold the new baby, shortly after the parents. No, they're not my kids, but I think it's holding that soft, sweet newborn that causes that flood of feeling. Not every set of parents encourages that on that first day, though, and that's their right. But if you didn't get to hold GD, right away, that may be why you didn't respond the same way you did to your own kids. Just a matter of circumstances, that's all.
As for now, I agree with others that it's GD's behavior you don't like, not GD. Still, I know it can be hard to distinguish between the two. When you find yourself thinking, "I really dislike GD" (or something like that), it may help to remind yourself of what you do like about her - her beautiful eyes, her affectionate hugs and kisses, her quick little mind, her... oh, she must have some redeeming factors!
It' s not unusual for GPs to be glad when their grands go home. But if you feel it that deeply, it may help to cut the visits shorter if you can.
Meanwhile, I agree with others about not saying anything. If DS can't even voice his childrearing opinions to DIL w/o getting shot down (poor guy - I feel for him), how much better/worse, do you think it would be for you? You could even find yourself cut off, if only temporarily. I know it's tempting to speak up, but, well... don't, please don't.