It's true that Meredith has sisters turning up like bad pennies, and she just gets more annoyed with every new half-sibling reveal. Lexie first arrives in season four, and Meredith outright rejects her. Meredith eventually comes around to Lexie, only to have her heart hardened when she dies. So, when Maggie shows up with more shared DNA, Meredith is cold. It takes Derek's nudging to melt Meredith into a begrudging compliance. None of this compares to her robbing her sisters-in-law of the chance to say goodbye to Derek as he lies on his deathbed. Amelia never forgives Meredith, and frankly, it doesn't seem like Meredith cares very much.
