Mrs. Van Daan is worried that the Franks have not yet arrived because she believes they have been picked up or taken by someone.
1. Lack of punctuality: Mrs. Van Daan is concerned because Mr. Frank had said they would be there at seven o'clock, and it is past that time. This suggests that Mrs. Van Daan is expecting them to be punctual and is worried that something may have happened to cause a delay.
2. Two miles to walk: Mr. Van Daan tries to reassure Mrs. Van Daan by explaining that they have two miles to walk, implying that it may take some time for them to reach the destination. However, Mrs. Van Daan does not seem convinced and jumps to the conclusion that they have been taken.
3. Fear of discovery: Mrs. Van Daan's statement, "They've been picked up. That's what's happened. They've been taken," indicates her fear that the Franks may have been discovered and captured by someone. This fear is rooted in the context of the story, where the characters are hiding during World War II, and being found by the wrong people could have serious consequences.
In summary, Mrs. Van Daan's worry about the Franks not arriving stems from her belief that they have been picked up or taken, possibly due to the danger they face as they hide during wartime.