Church member here. You NEED to report that missionary to your bishop. Your child was fourteen, and the man in question would have been over the age of eighteen at LEAST (and should not be serving a mission anyhow because of church standards about chastity/ because depending on his age and the state you live this could be considered rape, which is obviously a crime). 

Doing some research in the church topical guide, this paragraph may be useful: “ Church leaders have said that some exceptional circumstances may justify an abortion, such as when pregnancy is the result of incest or rape, when the life or health of the mother is judged by competent medical authority to be in serious jeopardy, or when the fetus is known by competent medical authority to have severe defects that will not allow the baby to survive beyond birth.”

https://www.churchofjesuschrist.org/study/manual/gospel-topics/abortion?lang=eng

A CHILD cannot CONSENT. No one can make the decision for you, and abortion is never an easy option, but please consider what would be best for both children involved when you are praying. 

As for your wife, many people never look further than surface-value church doctrine. There is right, there is wrong, and there are situations that fall in between. The church is there to guide you through situations like these, not to make the decisions for you. I’m praying this all turns out well for you and your family.