Supergirl #18 (2007)

The newcomer Supergirl accusses Kara from being a pathetic impersonator who stole her life and engages her. Kara fights back, as pointing out the real Supergirl would be focused on fixing the mess with the Phantom Zone ghosts, but her doppelganger is too strong. Kara is punched in the way of a subway car which crashes into her invulnerable body. Kara gets horrified by the sight of people dying, and confused when they vanish without a trace. Supergirl grabs Kara and flies her to Metropolis Centennial Park, the whole time claiming she's clearly an anomaly because she's too messed in the head to be Supergirl. As tossing Kara on the base of the statues of Superman and Superboy, her doppelganger states a screwed-up failure like herself could never stand side by side with both heroes or save anybody. Kara mutters she tried. She fought against everything inside her to be deserving of her cousin's trust. Her duplicate replies Kara isn't just made to be a hero, but she can make things right if Kara steps aside. The second Supergirl stretches her hand out. Kara touches it and starts dissolving into her doppelganger, muttering about her life plagued of regrets. Once she's faded, the second Supergirl flies away, but then Kara bursts out of her, shouting the real Supergirl never gives up. She makes mistakes all the time but she always tries again. The shattered remains of her doppelganger merge back together, morphing into a completely different-looking woman, determined to prove Supergirl is a cancerous cosmic anomaly. The landscape around them gets shattered, revealing the space void surrounding them, and Kara feels the crystals jutting from her body have disappeared. The woman attacks Kara, shouting Supergirl will fail her test. Realising the red Sun and the phantoms were part of a test, Kara gets mad and fights back, demanding to know why that woman is messing with her life. All of sudden a Monitor shows up and shoves the woman back as apologizing to Kara for his agent's behavior and declaring the test is over. Kara demands an explanation again, and the Monitor explains his brethen keep watch over the Multiverse, identifying and eliminating anomalies that might lead to their collapse such like Kara Zor-El (Earth-One) herself, who was supposed to die in the Crisis but was alive. Dark Angel was one of their agents, tasked with investigating Supergirl, but she became obsessed with proving the Girl of Steel was a dangerous anomaly which was to be eradicated. When the Fatherbox exploded, Dark Angel secured Supergirl in deep space, and one of her helpers, posing as Zor-El, created that phantom-plagued illusory world in order to force Supergirl to undergo her final test. The Monitor assures they'll not trouble her anymore. Dark Angel still begs for a last test but the Monitor angrily declares her present mission is over. As they fade away, the Monitor reiterates Kara can live her own life now. A dejected Kara notes she's been left in the middle of nowhere, but at least the Sun is yellow again. She decides to head back to Earth when she's unexpectedly approached by another stranger.