What is the difference between Femina and Mulier?
Mulier also can be used to mean "wife" or "mature woman" as opposed to virgo. In that sense, you'll find it more synonymous with coniunx as opposed to femina, which mostly suggests a female of any age.
How to say I am a woman in Latin?
"Ego femina sum" would be a more "standard" word order, "ego sum femina" changes the emphasis.