Perhaps Mrs. Evans had become especially dependent on Melody. After losing her real daughter, she might have clung to Melody for emotional stability, and that reliance had slowly turned into habit. Even now, it was clear she still harbored lingering attachment and dependency toward Melody.
Yes, the Evans were disappointed in Melody, but that disappointment hadn't yet reached the threshold where they could bring themselves to let her go. Still, as one letdown followed another, their feelings were beginning to shift—subtly, gradually, the distance was growing.
The one truly struggling to let go was Mrs. Evans. Her emotional dependence on Melody made it hard for her to cut ties. Her husband, on the other hand, was more concerned for his wife's well-being than for Melody herself. Their sons, however, had already started trying to curry favor with Kisha. Ethan was the best example.