Based on your description, the boy’s mother may have symptoms consistent with a psychotic disorder. Please bear in mind that I cannot confidently offer a diagnosis over the Internet. To make an accurate diagnosis, I would have to interview her in person but based on your description of her symptoms, a psychotic disorder is a reasonable conclusion. Believing that she is being spied upon (paranoia) and communicated with (magical thinking) are common symptoms of psychosis.
You find it “sick… that she’s using a nonverbal child and putting him in this situation.” It is important to understand that if she is psychotic, this is not willful behavior on her part. Just as it is impossible to intentionally develop symptoms of cancer, it is equally impossible to intentionally develop symptoms of psychosis. No one chooses to become psychotic.
Having said that, I believe that your concerns are valid. You worry about whether or not her behavior is negatively impacting her child. In addition, you understandably want to ensure the well-being of your child. The boy’s mother is displaying bizarre symptoms and you want your son to be protected. This is perfectly reasonable and understandable.
With regard to your specific question about how to get her to see that she needs help, this will likely be very difficult. It might be better to bring your concerns to the attention of her husband. Let him know about the behavior that you have witnessed and your concerns. As an acquaintance of the family, there is little else that you can do.
One way to assist the family would be to make them aware of resources such as the National Alliance for Mental Illness (NAMI). NAMI is great because they provide much-needed guidance and education for family members who have a loved one with a mental illness. They can also assist families who are trying to navigate the mental health system.
It is a troubling situation for all involved. Mental illness affects millions of people. When a loved one has a mental illness it is not just the individual with the mental illness who suffers but friends and family as well. Hopefully, your friend and her family will receive the proper help. I wish you the best. Please take care.