You can call a married woman “妇人”,but you know ,in my daily life ,I just call anybody who looks in her thirties and more or looks like married “妇人”,and accroding to the modern Chinese dictionary,“妇人”or “妇女”just mean woman who is older than a certain age whether she's not married or not,but acrroding to baidu,“妇人”means married woman in the past. For a writer like 沈从文 and a book written in the old times,“妇人” can have many meanings.I think you must connect the poilt to decide which meaning it is.In your example(I found the original passage),it does means married woman because “丈夫” was mentioned before.But sometimes “妇人” just means woman or an image of those poor women who struggle to live their lives.