If it's not something physiological, bed wetting is often found to be a manifestation of deep emotional turmoil... like sexual abuse. And, basically... it's a child's way of saying,
"stay away from me." If you feel that you need to act on any suspicions of child abuse and/ or neglect, you might want to start by contacting the local department of Child Protective Services in the city where your grand-daughter lives.
All I can say is when I was been sexually abused as a child at ages 7 to 10 I started wetting the bed,this lasted after the abuse stopped into my early teens.You need to talk to your granddaughter,gently,be careful,maybe it would be better if you can get her to a professional who knows how to deal with this sort of thing the right way.
Denise
I meant to add that a chat about it with your daughter ,her mom may be in order tell her you are concerned .Is there a Dad around to talk to ..
This is a tough one and I do appreciate that you are as a grandmom concerned for her, did she herself telling she has been doing this? when you see her next is there a way you can open up a conversation , only about her not introducing any comments about the 18 year old, ask your granddaughter how she is , how is school going ,if the issue comes up find out any reason she is wetting herself. Suggest to her Mom that she visits the Doctor as there may be a bladder infection ..It is good you are looking out for her ,it is possible you need further information. Good luck