How to break your child out of their manipulative streak?

Context: my stepdaughter is just turning 4 and couldn't be sweeter when you're around and playing with her and even just coexisting near each other. She is wonderfully behaved and affectionate, but the second someone she likes says they're leaving, including her dad or I, she gets withholding of her affectionate and will stop giving hugs or kisses that she was happy to give a few minutes prior. She gets grumpy and quiet and stares at you while you're putting on your coat. You can explain that she isn't going to see you again for a week or even just that you're going to the store and will be right back. Either one gets the same reaction--angry silence and a refusal to even say "goodbye".My question is how can we get her to break this habit? It hurts Grandma and Grandpa I think because they just want to show her love. I'm makes leaving the house difficult. I know she still loves these people very much, I just wish we could teach her how to express her sadness that they're leaving healthily and not in a manipulative, hurtful way. Any ideas? via /r/Parenting https://ift.tt/2JuWcTi