Then she's a widow.
But what if her husband/ex-husband's whereabouts aren't known to the reporter? The fact that she is a single mother is pertinent to the story. How she got to be a single mother isn't. As I mentioned before, there are many more things to complain about the MSM other than the term "single mother" which is the predominant usage everywhere in the United States that I have been to.
Complaining about the term "single mother" is silly anyway. Language evolves - that is the nature of language. The way the majority of Americans today would refer to a currently unmarried woman with a child would be to use the term "single mother." That's what I would expect a newspaper to use.