I don't get why this sentence is structured this way. The subject cant be a mother is she isn't female and yet it is steuctured so. The mother is a woman. This would work better as "The woman is a mother." Silly silly duolingo.
I don't think it's a language duolingo has made up though? This is the language structure
I guess it could be used for emphasis. "The mother [does this or that] because she's a woman."