What happened to Annemarie's sister, Lise, in Number the Stars?

Annemarie Johansen's older sister, named Kirsten Elizabeth and called Lise by her family, died mysteriously one rainy night after having been struck by a vehicle.

In Chapter 5 of Lois Lowry's Number the Stars, little Ellen Rosen, the young Jewish friend of Annemarie, has come to spend the night with the Johansens while the Nazis search for her parents, who have fled their home and hidden. Annemarie's father tells the two girls to put on their nightgowns and get into the bed where they may talk and giggle as sisters would. While in her bedroom, then, Ellen asks Annemarie,

"How did your sister die, Annemarie?"
"She and Peter [her fiancé] were out somewhere together, and then there was a telephone call that there had been an accident....Mama and Papa rushed to the hospital....When my parents came home in the middle of the night....they told me Lise had died."

She was struck by a car, and Annemarie tells Ellen that she believes the cause of the accident was partly due to the rain and slippery conditions.
 
Not long after this conversation, brutal German officers arrive at the Johansen home, demanding to know where the Rosens are. Calmly, Mrs. Johansen responds that they are probably sleeping in their beds since it is four o'clock in the morning. The harsh officer informs Mr. and Mrs. Johansen that the Rosens are gone, suggesting that the Johansens may be hiding them. Then this officer demands that the children come out of the bedroom. Quickly, Annemarie tells Ellen to remove her Star of David locket from her neck; when Ellen cannot undo it, Annemarie hurriedly rips it off Ellen's neck and clenches it in her own hand.

After the girls come out of the bedroom, an officer suspects that Ellen does not belong to the Johansens because the other girls are blond. Quickly, Mr. Johansen goes to the photo album and tears baby pictures from it. He shows the officer Lise's baby picture in which the girl has dark curls, just as Ellen does.

This poignant scene provides the loss of their beloved daughter Lise some meaning for the Johansens, who remove suspicion from Ellen with the quick thinking of the father.

Further in the narrative, Annemarie's Uncle Henrik is instrumental in smuggling the Rosens to Sweden. Unfortunately, Peter, who is in the Danish Resistance, is captured and executed in the square at Ryvagen in Copenhagen. When the Johansens visit the place near this square where the Resistance fighters have been buried with only numbers above their graves, Mr. Johansen reveals that Lise, Peter's fiancée, also was a member of the Resistance. Annemarie's father tells her,

"She was with Peter in a cellar where they held secret meetings. When the Nazis learned of this place, they held a raid. The members of the Resistance ran in every direction in their efforts to escape."

Some were shot--Mr. Johansen reminds his daughter that Peter's arm was wrapped at the funeral and he kept on his coat and hat in order to hide his distinctive red hair. During the flight of the Resistance members, Lise rushed into the street in order to escape; however, soldiers spotted her, and with their military vehicle, they ran her down.

After learning of the tragic death of her beloved sister, Annemarie returns home, opens the blue trunk and pulls the yellowing dress from the chest. Inside the folds of the dress she finds Ellen's gold locket. She asks her father if he can fix the lock so that she can wear it until Ellen can return.