In the Multiverse there are times when the right circumstances, and even people, can be replicated precisely on the same plane of existence. This is never more evident than the case of Lesla-Lar and her twin Kara!
In the bottled city of Kandor was a noted scientist, Lesla-Lar, who had observed the secret heroics of Supergirl aka Kara Zor-El, and grew envious at her potential for greater notoriety than Lar herself. Using one device to strip Kara of her abilities, and another to switch places with her temporarily, Lesla sought to besmirch the reputation of the Maiden of Might at the start of her career. As the second Supergirl, her public feats of goodwill masked her hidden contempt for humanity, for Superman, and for her lookalike Zor-El. At one point, this femme fatale actually allied herself with arch-enemy to Kryptonians everywhere, Lex Luthor... in a bid for power.
After being discovered by her city's authorities, she sought other means of vanquishing Supergirl with the aid of Phantom Zone prisoners. Alas, they turned on her and destroyed her using Kyrptonian weaponry. Or did they? Turns out, Lesla would return to torment Supergirl time-and-time again for years to come before revealing herself once more as who she now was.
Meanwhile, on Earth-Two there never was a surviving city of Kandor, only the virtual one within Kara Zor-L's Symbioship. And within that fabricated dream reality was the ship's construct of what it envisioned Kara Zor-L should be instead of the woman she turned out to be. A wife and mother with an infant, this Kandorian was the altered ego of the Kara who existed during part of her (just under) sixty-year voyage across the cosmos in her vessel. A war of minds occurred between Power Girl and the Symbioship's version of her similar to that between Lesla-Lar and Supergirl around the same time period a universe away. Transformed into an energy being, Lesla adopted different aliases before finally confronting her arch-enemy. In the end, Lar finally perished when her will proved inferior to her arch-enemy's during the height of their conflict.
As such, the counterpart of Lesla-Lar was the virtual Kara Les-Lar of the Symbioship, who like her doppleganger in the Earth-One universe never existed as a fully constituted individual while on Earth-Two... Lesla was a microscopic entity in Kandor such as her cosmic twin was a microscopic synapse within Power Girl. Only when the Girls of Steel and their Kandorian lookalikes traded placed in the physical world did the latter ladies exist among humanity.