Because they can be prepared when of if the Germans come and search the house.
Ellen promised Annemarie that she would pretend to be Lise, Annemarie's older sister, if the soldiers ever asked. This was to protect Ellen from being discovered as Jewish during the time of the Nazi occupation in Denmark.
Annemarie didn't tell Ellen the truth about Aunt Birte because it was a dangerous secret that could put Ellen's life at risk. The less Ellen knew about the situation, the safer she would be. Annemarie was trying to protect Ellen from the dangers of the Nazi occupation.
Annemarie promised Ellen that she would keep her friendship and hide the fact that Ellen was Jewish. She also promised to help Ellen escape to safety when the Nazis started targeting Jewish people.
Ellen spends the night with Annemarie because she is Jewish and the Nazi's are rounding up the Jewish people to send them to concentration camps. Ellen's parents send her to the Johansen's to pose as Annemarie's sister (who died several years prior before the book takes place).
She ripped off Ellen's necklace because if the soldiers saw the necklace they would know that Ellen was Jewish. If they saw that she was Jewish, they would have probably taken her away. She hid the necklace so the soldiers wouldn't find it. Again, if they found the necklace there would be a problem.
Ellen didn't smile when she looked at Annemarie during the fake funeral because she was in a different world.
The problem is that Annemarie's friend, Ellen who is jew would be relocated by the Nazi soldiers during the World War II.
Annemarie fell asleep while waiting for her mother.
Annemarie is afraid that Kristi might blow their cover and say something stupid like, "This is our friend Ellen and it's her New Year!". They had to pretend to be a family so saying that Ellen was a friend, could get them in a lot of trouble and only the Jews celebrated New Year's at that time, so it would have been too obvious that they're trying to help her escape. But she didn't. Instead, she talks about her new shoes.
Annmarie and Ellen needed to pretend they were sisters to protect Ellen's identity during a time of danger, likely due to the war or oppressive circumstances they were facing. This deception helped them avoid suspicion and potential capture by enemies or authorities. By presenting themselves as siblings, they could maintain a semblance of safety and support while navigating their perilous situation.
1: Annemarie, Ellen and Kirsti are walking and then they find 2 soldiers on the corner of the street. 2: The soldiers found out all the names of the Jews. 3: Ellen came to stay with Annemarie because it was said that soldiers would come to her house. 4: Ellen had to pretend to be Lise when the soldiers came to Annemarie's house. 5: When the soldiers come to Annemarie's house, Annemarie yanks Ellen's necklace off so the soldiers wouldn't think she was a Jew and then it gave her hand a mark, because of holding it so tight.
Annmarie and Ellen pretended to be sisters in order to deceive the Nazis and protect Ellen, who was Jewish, from being captured and sent to a concentration camp during World War II. Presenting themselves as sisters helped them navigate dangerous situations and hide Ellen's true identity.