Okay my grandma died last Monday and fr the past 3 days I've been having nightmares about her. My dream is, ill be laying in my bed sleeping, and my door will creek open and ill just be like kitty come here because ill think it was my cat opening the door but its her. She was usually smiling when she was alive but NOT in my dream. She would have a scary face and underneath her eyes were like Black bags like she hasn't slept in forever. But anyway.. Then ill say "grandma?" And she'll walk towards me slowly looking so scary. And I can't believe this dream is making me scared of my own grandma! But then ill wake up. What does this mean someone please tell me :(

It probably means that you feel guilty, a very normal reaction most of us have, even when someone we love was elderly. It means you are a good person who wishes you had said more and done more while she was alive. No matter how loving we were and how much we did, we often feel that we could have done more nice sweet things, and also done something to prevent their death.
Talk to her as you go about the house. Bring out some pictures and sit on the couch and pretend she is right next to you. Plant some flowers or a little shrub in her name. Talk to the rest of the family about this and about her. Say goodnight to her when you go to sleep.