Was my grandmother's dead sister real or another entity?

My grandmother(1900-1997)told my mother that when she was 6 years old, her younger sister who was four died of tuberculosis.This happened in a time when Puerto Rico in the old days Catholicism and Spiritism were predominant and walked hand-in-hand. A lot of Puerto Ricans saw spirits of the dead in those days. My grandmother said that a month after her sister's death she began to appear every midnight to see grandmother when she was a six year old girl. My grandmother's foster parents wondered why they heard voices of conversation and at times they would go to grandmother's room and see grandmother but no one else. But in time they began to see grandmother sort of pale for lack of sleep until the morning when she could go to sleep. Grandmother said that one night her sister said if she would like to join her in a place better than this. Grandmother gladly said yes. In time she began to get sick. One night she asked,"Tell me what is heaven like? What does God look like? What does Jesus look like?" Her sister immediately vanished from her eyes. After that, she never saw her sister again just because she asked her that question. Now...was that girl her real sister or another entity impersonating her?