Chloe Sullivan created a false backstory for the authorities to cover Kara's sudden appearance in Smallville, explaining that she was Clark's cousin on his adoptive father's side, raised in Minnesota for the past 19 years until she was able to track down her one remaining blood relative.
Kara became a target for Brainiac, who forced her to follow him into space. Brainiac trapped her on Krypton in 1986 after traveling through time. Kara appeared to return to Earth with Clark but in reality, Brainiac had put Kara in the Phantom Zone and was posing as her on Earth. Chloe rescued eventually both Clark and Kara from the Phantom Zone.
In 2010, Kara returned to Metropolis, publicly revealing her powers and becoming a hero to look after the city as the "Maiden of Might", keeping it safe from the "Darkness" that Jor-El warned Clark about. When the Vigilante Registration Act was put into effect, many heroes were put on a most wanted list. Among them was Kara, who was listed under the name "Supergirl".
After Clark was ready to face the darkness, Jor-El coldly informed Kara that her destiny was elsewhere. Tearfully, Kara bid Clark an unheard goodbye before putting on a Legion ring and disappearing, presumably to the future, to fulfill her own destiny.
Kara in Season SevenAdded by Kal-ELKara is a medium-tall woman with blonde hair and blue eyes, and has stayed the same age since she was stuck in suspended animation for 18 years and has an attractive appearance of a teenage girl. She, like her cousin Clark, wears primary colors of red, blue, and yellow in all of her clothing. When she lost her memories, she wore white most of the time until her memories and powers were restored. Kara in Season TenAdded by David KaiqueShe always wears her Kryptonian bracelet and also a Kryptonian necklace which both hold the symbol for the House of El. 
When she was trapped in the Phantom Zone, she wore black, tattered clothing and her hair was arranged differently in order to combat the Zoners.
When Kara returned, she wore a blue, leather jacket with yellow stripes on the wrists, with a yellow shirt underneath, and a pair of red jeans. As a super-hero, her costume is a light blue, long sleeved shirt, with a red skirt, and red boots with yellow stripes. When in disguise as a "civilian", she wears a brunette wig with glasses to keep herself undercover from the public.
- "I guess the humans are right, Kal-El. Girls do mature faster than boys." - Kara Kent, to Clark Kent, Kara
As a Kryptonian, Kara has many powers and abilities, like her cousin Clark Kent under a yellow sun. Kara's X-ray visionAdded by ImperiexSeed*Solar battery: This ability is the primary core from which all of Kara's superhuman powers and abilities manifest from. The interior of her body stores vast amounts of sunlight that gets emitted Earth's yellow sun inside her cells, and seems to operate like a battery.
- Super strength: Kara is extremely, almost astronomically powerful, being strong enough to pick up vehicles, trees, carts, metal, and wood without any effort. She is strong enough to fight Clark.. She later destroyed a impenetrable wall. She held up a billboard with one hand while in flight. (Kara,Fierce, Lara, Supergirl)
- Super speed: Kara can move and or react at alarming speeds that far exceed the sound barrier.
- Super stamina: Kara can take part in extensive strenuous physical action for long periods of time before tiring.(Kara)
- Invulnerability: Kara is is virtually indestructible, as she is resistant to all forms of physical and mental types of harm unless kryptonite is involved.
- Flight: Kara can easily defy gravity, as she has already mastered this ability, even though she has fewer years of experience than Clark. Also, Kara can fly into space in a matter of seconds. She can fly fast enough to grab a falling billboard, then quickly speed away in flight. She can also hover in mid-air. (Bizarro, Kara, Veritas, Supergirl, Prophecy)
- Telescopic vision: Kara can see objects and people from far away; she can even focus on particular earthly objects from space. (Kara)
- Super hearing: Kara can hear, whispers, frequencies, pitches, and other sounds that the human ear can't detect. She was able to recognize the sound of her distant ship's beacon. She was also able to hear that Gordon Godfrey was being possessed by Darkseid. (Kara, Supergirl)
- X-ray vision: Kara can see through any matter and material unless it is covered in lead. She first used her x-ray vision to analyze the inside of a mysterious time capsule. (Fierce)
Kara destroys kryptonite with her heat vision
(click for animation)Added by Babygogeta*Heat vision: Kara has shown more significant mastery and skill with Heat Vision over some of her other powers. However, at first she couldn't control this ability, sending out large pulses of heat. She later learned how to control it when she used it to save Clark. (Fierce) She later used it to destroy the control panel to Clark's kryptonite cage.(Traveler)
- Longevity: In an alternate reality Jor-El transported Clark to, Kara hadn't been kept in suspended animation for 18 years, and she still looked much younger than a woman in her early 40's. (Apocalypse)
- Super breath: The ability to use super breath to blow objects or people away. 
- Omni-lingual: Kara can read and speak many different languages like English, alien  and even Apokoliptian.(Prophecy)