this dream is not mine but my aunt's dream.. the dream is like this, she saw my grandma in her dream and her head falls off the body. then when she saw this she tried putting it back on her neck until she walk up from her dream. my grandmother was already dead about 3 months when she dreamed of this.

Was your grandma your aunt who had the dream's mother?

At three months, your aunt is still grieving, so in her dreams she could be trying to put your grandmother back the way she was before.

Did your grandmother die of something involving her head or brain, like a stroke?