I want to make an additional remark to my previous reply: It may be wise to tell your wife that you don't like her to work with brothers in fieldservice. Tell her that If she is going to do fieldservice, then working with sisters only.
I think a lot of us know the stories...brother x and sister y....working together in FS... getting to know eachother...What better opportunity there is to get to know eachother, you have to spend an hour or two and there's nothing else to talk about...I mean, really, who talks about bible verses in FS??
I know those stories in my own neighbourhood. So when I quit preaching years ago, I told my husband that I did NOT want him to go out in FS with other sisters. The fact that I no longer go out in FS does NOT mean he can work with other females, old, young whatever. He's still my husband.
It works well. Last month some brother who forgot about this (or didn't know, yet) wanted him to work with a sister and he said: "No, my wife doesn't want me to and I don't want to get in trouble."
Of course that is, if you want to save your marriage.