Ela tentou mais ou menos.
Na história do Super-homem de 2012/2013, H'El on Earth , Supergirl é cortejada por um kryptoniano chamado H'El e está convencido a tentar voltar no tempo para impedir a destruição de Krypton. Infelizmente, o método de viagem no tempo de H'El envolve a criação de uma explosão grande o suficiente para acabar com todo o sistema solar.
Supergirl desempenha um papel fundamental no avanço dos objetivos de H'El, mas recupera o juízo no final da história e esfaqueia H'El com um fragmento de Kryptonita, matando-o.
Ou então eles pensam.
As coisas ficam um pouco malucas depois disso. O arco da história de H'El on Earth termina aqui e o arco de Krypton retorna começa. Basicamente, Superman, Superboy e Supergirl viajam a tempo de pré-explodir Krypton para impedir que H'El evite a destruição de Krypton (e escravizar sua população no processo).
A coisa importante a lembrar aqui é que a história ilustra a importância de manter o fluxo de tempo e manter a história de ficar todo mucked up. Uma parte importante da história gira em torno do tempo de H'El alterando causando o fim do universo.
Vou postar a sinopse Banco de Dados da DC Comics aqui se você estiver interessado:
Superman has been pulled into outer space by an unknown force. There, he meets up with Superboy and Supergirl. The three meet the Oracle, who explains them that H'El, who survived their earlier encounter, has managed to bring Krypton back to life. However, H'El also altered the timeline and they must stop him from destroying the universe. With the help of Faora, the Oracle's servant, the three heroes travel to different points of Krypton's history to stop H'El's plans. Superman travels to Kryptonopolis a few months before Krypton's destruction, where he meets his mother Lara.
At first, Lara confuses Superman for an intruder and attacks him but stops after seeing the symbol of El in his armor. She also detects yellow sun radiation in his body and says he should wait for Jor-El. Superman watches Lara tell Jor-El that she is pregnant, but then his armor changes back to its usual colors. In that moment, Superman confronts a mysterious person who is aware about his travel in time.
This stranger is in fact Jor-El, who came from one of the alternate futures created by H'El. Realizing he was the one who created H'El, Jor-El has come to the past to stop H'El from conquering Krypton. Superman and Jor-El travel to Krypton's core and fight H'El. At first, Jor-El wants to kill H'El but Superman instead uses H'El's own chronal powers against him and freezes him with his super-breath, locking H'El in a state of eternal limbo. As Superman and Supergirl are reunited in the present, the Oracle informs them that Superboy sacrificed his life to stop H'El. Mourning the loss of their friend, Superman and Supergirl return to Earth.