There is no official position within the church known as "the preacher's wife." Hence, there are no requirements placed upon her that you would not find placed upon any Christian woman.
Those who serve as evangelists have the right to marry. "Do we have no right to take along a believing wife, as do also the other apostles, the brothers of the Lord, and Cephas?" (I Corinthians 9:5). Notice that Paul didn't say they had a right to a wife. He said they had a right to a believing wife. A preacher's wife must be a Christian. Why? A preacher represents the church and the Lord. It is his duty to teach others the gospel. If his own wife will not believe the gospel, what impact will that make on his teaching?
A preacher also has the right to bring his wife along with him as he journeys in teaching the gospel. Some preachers settle into an area to work, such as Philip (Acts 21:8) who appears to have stayed in the Caesarea area for over twenty years, but many travel from region to region in their work. Especially when working in foreign fields, it is wonderful to have a companion to be with you and who can help keep the home while you are off teaching the gospel. She can take care of the daily chores, such as locating food in a foreign market. If you ever been to a foreign country for any length of time, you know how pleasant it is to find someone who can simply speak your own language. A preacher's wife can set up a haven of rest for her weary husband, even if the fields in which he works are close to home or far away.
Before I sought out work as a full-time preacher, I asked my wife and my children if they were willing to accept the responsibility. Like it or not, people see the preacher as a leader and a representative of the congregation. His wife and his children will be expected to set a proper example of Christian behavior at all times. While elders and deacon's families must display certain qualities, a preacher's family must develop them. "Likewise their wives must be reverent, not slanderers, temperate, faithful in all things" (I Timothy 3:11).
Far too many Christians see problems, but all they do is grumble about them. Preachers are called upon to see that problems are fixed in accordance to God's word. Hence, there is no grumbling about the lack of hospitality in a congregation. The preacher and his family demonstrate hospitality so others will learn. There is no complaining about the lack of Bible teachers. The preacher and his wife are first in line, showing an eagerness to teach others.
Perhaps the most difficult thing for a wife of a preacher to learn is the willingness to share her husband with others. Preachers keep odd hours. They are called upon when a death occurs at 4 am. They run off to Bible studies on a moment's notice, even though dinner is cooling at home. It can be perplexing being married to someone who would rather talk than eat or sleep.
Then too, you must realize that most preachers are not paid well and what pay they get is often suddenly reduced because a supporting congregation halfway across the country lost too many members. I was blessed to have found a wife who is extremely frugal. We live to our best of our ability with minimal debt. My wife stretches the budget to the extreme. We've never managed to save much. We learned over the years that you really need a pad in your savings account so that emergencies don't cause you to incur debt. Nothing eats up income like interest on debt. However, that means you have to be willing to put off purchases until you saved up for them in advance. It means waiting a year or more for that new sofa. It means driving an old car. And it means shopping at Goodwill.