This one's a downer—don't say we didn't warn you. Ready?
After Lise's death, her parents keep all her stuff hidden in a trunk:
In the blue carved trunk in the corner of this bedroom—Annemarie could see its shape even in the dark—were folded Lise's pillowcases with their crocheted edges, her wedding dress with its hand-embroidered neckline, unworn, and the yellow dress that she had worn and danced in, with its full skirt flying, at the party celebrating her engagement to Peter. (2.42)
All of these items—especially the dresses she wore (and planned to wear) to celebrate this oh-so-happy occasion—are a painful reminder that Lise herself is gone. Her parents just hide her things away and try not to think about her death. Annemarie, on the other hand, likes to look through Lise's trunk. And actually, this habit gives the trunk some eerie parallels to Great-aunt Birte's casket, which is also full of clothes.
By keeping Ellen's Star of David necklace in Lise's trousseau, Annemarie also creates a bond between Lise, her biological sister, and Ellen, her new kind-of sister. Of course, there's one big difference: when the war is over, Annemarie will be able to open the trunk and reclaim the necklace (and she'll be able to see Ellen again, too). Lise, on the other hand, will never come back.
But we're hopeful about one thing: after the war, Annemarie's parents are more willing to remember Lise again. Before, they just tried to hide their pain from Annemarie. They even tried to make up for what happened in the past by keeping Ellen safe in a way that they couldn't keep their real daughter safe. But once the reality of the war that killed their daughter is further behind them, they might be able to accept Lise's death and begin to heal.