Ego sum femina still sounds redundant. It's a pretty rough way of translation without considering the standard Latin word order and omission (or earlier, non-existence) of personal pronouns. When you're asked to translate "I am a woman", all the versions should be accepted, but when you're asked to translate it as "I am a woman" from Latin, the sentence in Latin should be "Femina sum" because that's the basic way of saying it and thereby the users can get used to word order. It is like that in all other languages, particularly Romance, all over Duolingo.
Feminine comes from the Latin, but it was borrowed from the French first.
History of the word:
Latin femina -> French féminin/féminine -> English feminine.
English is NOT a Latin language. (not directly)
It's very specific to the French language, when latin uses "us", or "a", or "o" as an ending, French simply drops this ending.
A way to know if it comes directly from Latin, or from French, it's when the words comes directly from Latin in English, (it's scarce, but it happens with law and medical vocabulary), it tends to keep its Latin ending (for instance in "a")
Fémin/féminine also gave "femme" (woman) and "femelle" in French,
and "female" derivated from the French "femelle".
I did some Latin in my highschool and I remember the verb is always at the end of the phrase, not after the subject. For instance, Femina sum -> I am a woman. ( FYI, I think woman is rather mulier than femina ) Also, as in my native language Romanian, the personal nouns are optional . It is not mandatory , as in English or French to add Ego or Tu in the sentence. The person can be detected in the verb
Indeed, I checked a frequency list, and mulier does indeed appear first, at least with non-lemmatic forms counted separately, at 1125, vs 2205 for femina. http://www.slu.edu/colleges/AS/languages/classical/latin/tchmat/grammar/vocabulary/hif1-ed2.html