I cannot be two women so in this case I think it makes more sense to leave out the article μία. It is a general statement of fact. Εγώ είμαι γυναίκα sound more natural.
Thank you, that is a valid point. I have added the sentence: "Εγώ είμαι γυναίκα." but have maintained "Εγώ είμαι μία γυναίκα." There are two reasons for this. The first is that without context the use of the definite article is not incorrect. The other is that as many learners have seen this sentence it might cause confusion to find it only without the article.
In addition, I have made similar alterations to: " "Εγώ είμαι ένας άντρας" and "Εγώ είμαι ένα κορίτσι."
Thank you for your input and we look forward to more. We are working on a new tree in which we hope to have corrected the errors found on this tree. Please see the forum site to a make suggests here
Thank you for the link, Jaye. Learners should now look at the right side for "New Tree--update on the progress" for a link to the latest from Dimitra, and to add their comments there.
Shouldn't "μια" be the right solution instead of "μία"? Or is the explanation in https://forum.duolingo.com/comment/17806268/%CE%BC%CE%AF%CE%B1-and-%CE%BC%CE%B9%CE%B1%3E not correct?