All missionaries do not serve in roles of ecclesiastical authority.
Even on church-planting teams, only one or two need to be elder-qualified men. While there is a great pressing need for more elder-qualified ordained men on the field, elder-qualified ordained men are not the only ones rightfully called missionary.
Most missionary teams are comprised of both men and women focusing on a variety of roles, from preaching to teaching women and children, to bible translation, literacy, medical care and education. All of these roles support the goal of discipling the nations.
The OPC is certainly not a loosey-goosey denomination in regards to ecclesiology and they have this to say: Q and A
So, NO, all missionaries need not be ordained elder-qualified men. We do need more of those types though. And YES, women make great missionaries and have, since Carey's day, comprised an average of 63-64% of the missionary work-force.
As you no doubt know, the term "missionary"' does not refer to a Biblical office. To be sure, those missionaries who have been ordained and called by Christ's church to serve as Evangelists or Teachers of the Word of God on a field will only be men. However, we also use the word "missionary" to refer men or women who have not been called as Evangelists or Teachers but who are appointed to diaconal service that is done alongside the preaching and teaching of God's Word.
Such service includes the medical service of doctors and nurses, Christian school teachers and administrators, and those who maintain the mission's facilities or who otherwise do that work which demonstrates the love of Christ to those who are the objects of the preaching of the Gospel. It is in this diaconal type work that the Committee on Foreign Missions of the OPC has found it appropriate to appoint non-ordained men and women to "missionary" service.
"If a commission by an earthly king is considered a honor, how can a commission by a Heavenly King be considered a sacrifice?"
-- David Livingstone