Viewers see Kara evolve from being reserved and somewhat timid to a genuine hero who won't back down from a fight, no matter the adversary. Central to the story is the sentiment that you shouldn't define yourself by how others see or relate to you. Instead, listen to what your heart tells you is your path. Some issues arise because of her gender (an argument over whether she should be called "Supergirl" or "Superwoman," for instance), but they're usually lighthearted. Integrity, self-control, and courage are important themes.
Supergirl faces off against sinister villains, and the physical clashes are intense and violent, enhanced by the players' super strength. Some scenes feature gun use (fortunately, Supergirl is inherently bulletproof) and other weapons as well. Even so, serious injuries are rare, but battles are frequent, including fistfights between men and (super) women.
Some flirting among adults; an important subplot centers around Supergirl/Kara's sister coming out as gay, same-sex kissing follows the reveal of her sexuality. Kara interrupts a couple having sex, but nothing sensitive is shown.
A few curse words in every show: "hell," "ass," "damn."
The series is related to the story of Superman, who's not visible but whose legacy is influential for Kara. Some episodes involve characters or plotlines from the shows Arrow and The Flash, which share common creators with Supergirl.
Drinking, Drugs & Smoking
In the show's second season, characters drink at bars and at home -- clinking glasses and chugging beers and glasses of wine to celebrate when good things happen.