At the risk of offending gay people who say they are born that way, not made that way:
I wonder if she was always left alone with the kids while he played super elder, with all the field service, meeting parts, shepherding calls, quick builds, hall cleaning, elder meetings and so on. If so, maybe she found a friend(s) who helped her get through her loneliness and realized she loved that friend who cared more about her than her husband did.
I've said that to JW's, I understand why a woman would leave a man in the organization (or any absentee man) for a woman, the companionship and mutual affection. Needless to say, I would get the evil eye.