Bleed'Em and Weep

Woman gets the drop on a bad guy, who is threatening either her or the good guy. Usually the bad guy doesn't believe she will shoot and makes a move. She shoots him, looks horrified at what she's done, drops the weapon and bursts into tears. Sometimes she collapses. Alternatively, she may just stand there holding the weapon, waiting for a man she trusts to snatch it out of her trembling hand. Half the time, after she drops the gun, the enemy then gets up (being just wounded) and the battle continues.

Quite often, before she actually does the deed, the woman is very shaky and hysterical (as opposed to a man in fiction, who merely holds the gun). Whereas a man would look down the barrel and coldly say "I'll kill you", a woman in fiction will point the gun with a hand quivering in rage/fear and scream "I'LL KILL YOU!" with tears running down her face.

This doesn't seem to be as prevalent as it used to be, possibly because there's less emphasis now on women being the 'weaker' sex and there are more 'Badass' female characters around.

If a similar thing happens to a male, it's generally portrayed as a Rite of Passage, something that makes a man out of him (see Upham in Saving Private Ryan, the son in A History of Violence). He doesn't drop the weapon and he doesn't cry. See A Real Man Is a Killer.

Anime and Manga

 * Battle Royale: Noriko Nakagawa bursts into tears when she kills Kazuo Kiriyama, even though he had slaughtered thirteen people previously.
 * In Highschool of the Dead, Saya Takagi breaks down for a moment after killing her first zombie.

Comic Books

 * Justice League the New Frontier: Shooting a North Korean is an extremely traumatic experience for fighter pilot Hal Jordan, who blames himself for not remembering how to say in Korean that the war was already over.

Film

 * Seen in the John Wayne movie, Rio Lobo. Amelita (Sherry Lansing) shoots a corrupt sheriff repeatedly (and very coldly), then breaks down sobbing afterwards, making the point that enduring physical pain and overcoming the emotional trauma of killing someone are very different things.
 * Shooter. Kate Mara repeatedly shoots Elias Koteas, who is implied to have raped her earlier. Koteas' character was able to get the drop on her after she blew his mook away with a sawed-off shotgun--and went into shock over it.
 * The Eye of the Needle (1981) ends with Kate Nelligan shooting Donald Sutherland (a Nazi spy who became her secret lover, only to murder her crippled husband and threaten the life of her young son when his cover was blown) to prevent him rowing out to a U-Boat with info about the impending D-Day landings. "I had to do it," she sobs, when reinforcements finally arrive (in a helicopter).
 * In The Getaway (1972), Ali Mc Graw stares aghast after emptying a Colt Model 1903 into the Big Bad. There are factors influencing her emotions:
 * The Jean Claude Van Damme movie Hard Target contains something of an aversion to this trope: Yancy Butler shoots one of the bad guy's henchmen and is admonished by the Van Damme character's Uncle Douvee (Wilford Brimley) for doing a man's work. He attempts to take the gun off her but she takes it back and walks grimly away.
 * In Legion there's a gender-flipped subversion. Jeep desperately wants to be able to shoot the bad guy because he wants to protect the MacGuffin Girl. But he can't. He ends up in the rest room sobbing and puking just from coming that close to firing a gun at someone.
 * In Ride Lonesome, Karen Steele's Determined Widow character points a rifle at the protagonists and tries to shoot, but Randolph Carter takes the weapon from her and convinces her that they're on her side.
 * In the Rob Zombie version of Halloween, Laurie
 * In Blade Runner, Rachel is very shaken after shooting Leon off Deckard.
 * In Unforgiven, the Schofield Kid breaks down crying (in a somewhat delayed reaction) after killing Quick Mike while the latter was using the outhouse. While he talks tough about his reputation as a stone-cold killer, this is actually his very first kill.

Literature

 * A variation exists in Foundation and Empire. A woman shoots a friend in order to stop him from talking (It Makes Sense in Context). Then she cries for the first time since her childhood.
 * Antoinette in The Prisoner of Zenda.

Live Action TV

 * The Professionals episode 'Runner' ends when a female character, played by Barbara Kellerman, shoots a bad guy (who killed her boyfriend earlier in the show) just before he kills one of the CI 5 agents. She weeps mascara tears.
 * In an episode of Sharpe, a woman begins the episode by taking a boat from Ireland, riding on horseback across war-torn Europe up to the front lines, bullying her cousin Wellington into letting her stay at the camp, and beating everyone except Sharpe himself in a marksmanship contest. Then, when forced to shoot a man in self-defense, she bawls like a baby (and makes out with Sharpe). Furthermore, when Sharpe tries to tell her she "proved herself," she protests that women prove themselves when they have babies.
 * In one episode of Charlie's Angels, one of the Angels loses her memory. A group of men attempt to steal her bag; she fights them off, eventually finding a gun in her struggles and pulling it on them to convince them to back off. Although she doesn't shoot anyone, as soon as the danger is over she drops the gun and runs crying down the beach.
 * Kimberly Bauer of 24 breaks out in tears when she shoots the man who attempted to kill her. More tears ensue when her father instructs her to shoot him again.
 * A Target Women segment parodies an "intervention"-themed clothing commercial by having Sarah shoot a friend to stop her from buying the wrong outfit, freak out, accidentally shoot the other friend she brought with her and then casually step over to the rack and start browsing.
 * Tessa does this in Highlander after she takes out a serial killer with her car.

Web Original

 * When Michael is knocked unconscious during the battle at the end of Were Alive's first season, Pegs is left defenseless when Latch and Scratch come looking for them - or so we think, until she picks up Michael's SMG and kills Latch with it, leaving Scratch emotionally scarred (they were twins, after all). So far, Pegs is still being haunted by what she had to do that night to save Michael.