I am the director of clinical research for our medical school campus. I agree that there is much to be done in research of the trauma of a chronic childhood illness and its effect on adult health, particularly mental health. I have personal experience with this as I have a now adult child with type 1 diabetes. In my opinion, the MPH route should get you the research foundation to get started quickly. The most important thing in research today is forming a multidisciplinary team. I would investigate your local medical school and/or college of public health to see who might be working in the field of trauma.
Would be happy to talk directly!