I'll say it again. These Mennonites are never going to change their stance on vaccines. Most are stuck with beliefs dating back to the early 1700s. Hell the couple in question with the six year old who died speak a broken English + Early 18th Century Low Germanic language.
These people are beyond back woods. Asking them to change is about as likely as having the sun set in the East. Their daughter dying from a preventable disease isn't some lack of prevention, to them it was the will of God.
You might as well walk up to a seven year old and ask them to perform triple bypass surgery. These people are unable to understand a vaccine. They lack the quantifiable knowledge to even begin to comprehend a vaccine.
People might ask how many of their children must die before they vaccinate. The answer is 100% of them. Likely fully explaining vaccines and microbiology to them would likely be seen as human arrogation in God's will. They would rather be wiped from the face of the Earth than to believe they have some sort of say over God's will.
That is the kind of people we are talking about here. They will unquestionably follow the "laws" of their religion even if it means the painful death of everyone they love. You CAN NOT CHANGE these people. It is impossible.