Personality:

Encompassing the idea of a strong sexy woman who knows her way around a gun, Zoe is a deadly soldier who kicks ass. A former Browncoat soldier (Independents who fought against the Alliance) who used to serve under Malcolm Reynolds, Zoe follows him under and is his second in command—she’s dependable, trustworthy, and loyal to Mal. She follows his orders, even those that land her on the wrong side of the law. However, she doesn’t follow these commands blindly; it was revealed that Mal was actually against her marriage to Wash, but she followed through with it anyway. She does have a tendency for dry humor and wit, both of which she many times uses at Mal’s expense.
Her loyalty is a benefit to the ship, as unlike Mal, she has a good head on her shoulders—thinking situations through before she engages in any type of action and even when in the midst of a fight, and she tends to be calm and collected during whatever situations Mal has gotten them into. She’s terse, as her husband describes her, and deals with issues as efficiently and composed as possible. In the episode “War Stories,” Zoe came to rescue both the Captain and her husband after they had been tortured. She barely reacts to the scene, only with repressed anger, even after their torturer gives her Mal’s severed ear. Zoe acts as Mal’s counter-balance as she tends to be the voice of reason and caution in times of panic; even if he goes against her advice, Zoe will follow as she has faith in her captain.
That’s not to say that Zoe is perfect—she sometimes has trouble juggling her loyalty to Mal along with her love for her husband. Although Wash seemed to get over her split loyalties, Zoe would some times internalize the wishes of Mal to become her own—something that would anger Wash, who wished for his wife to be independent more often. Despite this, Zoe is still a good wife, and they have a good marriage. Who takes the dominant role in the marriage isn’t always obvious, as she sometimes takes a more aggressive stance in the marriage, but it’s a marriage built on mutual love and respect. Trust me, she really loves her husband.

Abilities and Weaknesses:

Zoe used to be career military, which gives her the skills of a soldier, a crack shot, and a very strong backbone. Her fighting abilities are amazing, as she’s pretty much always using them. She has the honed senses of someone who never really left fighting behind them. She also knows field first aid.

Her weaknesses probably start with her loyalty, and the friction it causes with her marriage, but essentially usually lead back to her husband. She tries to ‘protect’ his feelings, but many times ends up in the doghouse with him.

Inventory: Some clothes—pants, shirts, vests (one of them bulletproof), and her favored brown duster coat. Also a few guns, notably her cut down pump action rifle.
Appearance: She’s a "fine good looking woman." Zoe is a dark-skinned woman with an athletic physique with curly brown hair. She usually dresses in pants and boots, her outfit complemented with a brown vest, jacket or coat—a residual show of respect for the Browncoat soldier she used to be.
Age: Early 30s.

OC/AU Justification ;
If AU, How is Your Version Different From Canon, and How Will That Come Across?
If OC, Did You Run Your Character Through a Mary-Sue Litmus Test?
And What Did You Score? HERP A DERP