女斗士 was used to pertain to a courageous female based on what I read, but I wanted to know how am I able to use this word and when?
So 女斗士 literally means “female warrior”. You would use this term the same way you use 斗士, since “female” is just an additional detail.
The coronavirus situation is globally rampant; nurses all over the world are fighting in the frontlines, just like female warriors, to ensure the safety of the people.
(I made the assumption that the vast majority of nurses are female)