To write the female hero, when she is not the primary hero (aka co-protagonist), the author must decide if this heroine will be given equal time to the hero in the story. Will she be equal in skills as a complement to the hero, or will her skill set be completely different to the hero's? Will she be the meeker character, have wisdom, be the flighty femme fatale, or will she be quite ordinary? Will she be a beauty, have sex appeal, be of a plainer appearance, or will she be a chameleon? Will her character be admirable, questionable, or cleverly concealed when she chooses to be mysterious?
Some of these inquiries will be affected by the genre.
Writing a heroine has perhaps even more options than writing a hero. Why do I propose that as a possibility? Heroes are simpler because men can be less complex in their psychological makeup. It's one of the things that make them so appealing: their focus, their visual predictabilities, their quick assessments of circumstances, and their desires to fix the wrongs in any situation - even if their initial assessments prove to be wrong - and even if the heroine in a story doesn't need or want it/them to be "fixed".
If a heroine is the main character, she must be given certain strength(s). She can't be too fragile, whiny, or a shell of a person - too unlikable and undeserving of "heroine" status. Having said that, she can be a quiet, unintrusive, injured by life but surviving character. However, if that is her nature, the author must work very hard to show her as capable and give her a quality or qualities to make her appealing and likable. Heroes and Heroines drive a story. Without them serving up something to enjoy and appreciate, favorably respond to, cherish or treasure, those words on the page will more than likely serve instead to irritate and disgust the reader. Those don't bode well for finishing the book.
In Then . . . you the heroine states:
"Stone, why are you helping me?" She asked it softly maybe because she needed to hear his answer but didn't want to nag him about it. "I mean, I show up on your porch, a sopping wet mess, running away from an abusive boyfriend, and here you are enjoying your tranquil life of solitude and doing what I know must be an important profession post-military. I doubt I've ever felt more stupid - or more desperate - and you just took me in without any condemnation and gave me immediate accommodation. . . ."
She wants something but doesn't want to demand it from the man who's helped her. Strength with consideration. Admiration and respect for him, a need requested from her.
So many options for authors creating their heroes and heroines . . .
Father, you give me mine. Thank you is never enough. Never will be. In the Name of Jesus, Amen.