a Kryptonian rocket lands on Earth, bringing 15 year-old Kara Zor-El, first cousin of Kal-El, from the Kryptonian colony on its moon, Argo.

Before Krypton perished, the scientist Zor-El, brother of Jor-El, built an indestructible, translucent dome over Argo City, where he lived with his wife, Alura, and daughter Kara.

When Krypton exploded, the moon, Argo, covered by the dome, was blown free of its orbit and survived, settling into a stable orbit around the giant red sun, Rao.  But soon, the remnant discovered they were being poisoned by radiation coming from the ground itself.

Knowing they did not have long to live, Zor-El used his brother’s plans to build a rocket for his daughter.  His wife would not leave without him, and he would not leave Argo City and its people behind.  It was meant to carry her to safety, on a world inhabited by descendants of Kryptonians who long ago left their homeworld to colonize other planets.

Instead, the rocket went through the same warp in space-time created with the destruction of Krypton as her cousin Jor-El, the puppy named Krypto, many chunks of Kryptonite and other assorted detritus of that world, and the Daxamite known as Mon-El.  This warp in space & time brought them all to Earth in the early 21st Century.

Kara’s rocket was discovered by Superman, and she recognized him as her cousin, Kal-El.

He hid her out by giving her the name of Linda Lee and having Lois Lane enroll her into the Midvale orphanage.  While there, she met Lena Thorul.  Supergirl learned that Lena was the sister of Lex Luthor.  Luthor begged Supergirl not to reveal this to Lena, and she agreed.

Eventually, Linda was adopted by Mr. and Mrs. Danvers, and she lived in Midvale with her new family.