Is what happened to my mother—her hearing a different voice claiming to be "the servant of the soil" and delivering a message from a deceased woman concerned about her children—real or not?

There is no evidence for the existence of a "servant of the grave," and what some believe about the presence of an angel or jinn serving the graves has no basis in truth. The deceased is cut off from this world and has no ability to attend to the affairs of their family due to the barzakh (definition) that separates them until the Day of Resurrection. A Muslim must maintain dhikr and ta'awwudhat (invocations for protection), and offer du'a (supplication) and sadaqah (definition) (charity) for the deceased, knowing that what one sees in a dream or what a person who has lost their mind imagines holds no weight.