Supergirl and the Legion of Superheroes #17 (Vol 5)

Adapting to the 31st Century, Supergirl perceives everything as a dream, a facet of a Kryptonian coming-of-age ritual. To validate her belief, she starts to exert her will, prompting certain events to unfold, such as receiving an offer to join the Legion. Meanwhile, the Dominators are devising a scheme to subjugate Earth once more, apparently dispatching an organism to carry out their nefarious plans.