Hi! It's great to hear from you again!
I am glad to hear that you fixed up your side of the porch and it worked for you. I had to laugh at how you phased it. I enjoy your sense of humor immensely.
I do agree with you. Boundaries are important to any child and developmentally, boundaries help a child feel secure. Providing boundaries is one of the toughest parts of parenting (as you already know, I'm sure) and it is especially important with a child with behavioral issues, such as your granddaughter. Does it mean she will stop the behavior? Probably not. But it will help control some of the aspects of her behavior and it will give you some measure of control, which can help you feel better.
This is a problem that you could work on with the behavioral therapists. They should have tons of ideas to help you and will also have the resources to set up a schedule and behavioral boundaries for your granddaughter. Each child has their own limitations and personalties so taking advantage of what they know about her will help you get the best plan possible.
Also, try a Star chart. List good behaviors such as chores (keeping her clothes picked up, picking up her own dishes, etc) and staying quiet while Grandmom is one the phone for example. Since I assume she cannot read yet, remind her of what is on the list on a daily basis. Then when she does something on the list, give her a reward. Place a star next to the good behavior then offer her a toy out of a basket you put together or offer her time to watch a favorite program. Anything you feel would work. This helps reinforce her good behavior and takes her away from the bad behavior.
Here are some more resources to help you find other ideas:
http://www.williams-syndrome.org/- if you don't know about this site already, it may have support for you in helping her.
Achieving Best Behavior for Children with Developmental Disabilities: A Step-by-Step Workbook for Parents and Carers by Pamela Faith Lewis
Parenting Children with ADHD: 10 Lessons That Medicine Cannot Teach (APA Lifetools) by Vincent J. Monastra
Let me know if I can help you any further.