In “Don’t Say Good Luck,” however, you’ll actually notice her. She’s matched beat for beat by Melanie Lynskey, no revelation but reliably affecting and emotionally generous as our heroine’s doting, ailing mother. The latest collaboration between Netflix and Adam Sandler‘s Happy Madison Productions, “Don’t Say Good Luck” is markedly more delicate and deeply felt than most films bearing that imprint, though it’s still proudly mainstream in sensibility — unafraid of sentimentality as it lunges directly and most effectively for viewers’ heartstrings. Her boisterous pre-teen twins Ethan and Caleb are too young to grasp quite what’s at stake; high school sophomore Sophie (Sandler) has rather more vivid memories of going through this anguish before. Commendably thoughtful and quietly humane for much of its running time, “Don’t Say Good Luck” also knows just when to let it out.