I do not have as much experience with the Type II as Type I. I do know that 300 is very high for Type II and she is gambling with her life if is continues in this range. How old is she?
Her mother is a negative influence on your W and a doctor or very good friend would probably reach her better. I doubt she'll listen to you. If her family makes her feel insignificant then she may be unconciously doing harm to herself due to such low self-esteem. The child should be the source of reason for her. She should want to live a healthy life to see him grow up, but if she's in denial....then she needs to be shocked awake. Some day, she will be....but at what price? A heart attack, a stroke, or worse?
Try not to compare how she responded to her friend and to you. Especially don't think anything of the son's TM b/c you know who was & wasn't behind both times. You're hurt and that magnifies everything.
You are tried and frustrated and it's hard to make decisions under those circumstances. I think you can look down the road and have some idea what life will hold with your W. You may have a better life apart from her and with another person, but then again who knows? Think of what's best for your child. Do what works....and do the right thing.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!