This was just after my mother's funeral and after all our visitors had left the house. The family was all sitting around and talking. Dad was at the head of the dining room table. Carrie was sitting to his right and I was to his left and we were all three turned to face the living room where everyone else was.
Kaitlyn was 2.5 yrs old at the time.  She was on the floor between me and my father and was laying on her back smiling.  She seemed to be focusing on somewhere between the floor and the ceiling - not on the ceiling.  She started waving and saying "Hi Grandma" just like my mother used to say to all her babies. Mom used to repeat it over and over to the babies so that they would learn how to say it back to her (I guess). 
She would also say repeatedly, "Ma-ma-ma-ma" to them.  Kaitlyn was saying "Hi Grandma" over and over and smiling away. I asked her if she could see Grandma and she nodded and I asked her where Grandma was and she pointed to where she was looking (Midway between floor and ceiling). 
I told her to blow Grandma kisses and she did and I asked her to say "I love you, Grandma" and she did. The light in the living room flickered once.
My sister-in-law, Carrie saw it all too.