My grandchild has sleep issues compounded by her disability and the birth of a new brother. What can I suggest to help the parents?
At one point in my career, I did developmental assessments on children 0-3 years of age who were suspected of having one or more disabilities. Many of them had very rare disorders such as the one your granddaughter has. I learned that these children often have many unusual behaviors (throughout their childhood years) that are related to the disorder and tend to be resistant to the usual behavioral interventions that work for typically developing children.
Therefore, as a first step, I suggest that you encourage your granddaughter’s parents to talk with her doctor about whether or not the sleeping problems she is having may be related to the disorder and if so, what can be done.
If not related to the disorder, it could be that she is having trouble adjusting to a new brother, as you had guessed. If this is the case, it will be important for her parents to establish a bedtime routine with her and to spend some special time with her (away from her brother), reading to her, singing to her, and stroking her gently as she falls asleep. Also, enlisting her to help with her brother can take her out of the position of competing with him and give her the opportunity to help him.
If it is fear that is keeping her from going to sleep, it is important to find out what she is afraid of and to learn what would help her cope with her fear. She may be able to tell you or her parents during the day, long before it is time to go to bed and before the fear builds up. Can you assign a favorite stuffed animal to help her feel safe or make up a concoction of monster repellent?
Once again, keep in mind that these common interventions may not be successful for your granddaughter because of her diagnosis. If that is the case, her pediatrician or a specialist who understands the diagnosis and treatment of the condition will be the best resource for her, her parents, and you.