Why is Mrs. Van Daan important to Anne Frank?

Mrs. Van Daan is important as an alternate mother figure to Anne, as Peter’s mother, and as a sower of discord in the attic.
In their early days of confinement, Anne feels pressured by the amount of time spent with her own family. Although they have to make adjustments to share the space with the Van Daans, the novelty of having others around is appealing to her. Anne finds Mrs. Van Daan a reassuring presence and feels a kind of emotional connection to this outgoing woman that is different than to her own mother.
As Anne and Peter become friends, it seems that Mrs. Van Daan resents Anne’s attention to him. This in turn makes Anne uncomfortable, so she becomes more distant from her. In addition, Anne cannot help but be aware of the older woman’s pettiness as she takes offense at trivial matters, such as Anne spilling milk on her coat. In such a small space, Mrs. Van Daan cannot make the right kinds of efforts to ensure peaceful coexistence, and Anne comes to appreciate her own mother more.

The Diary of a Young Girl is a true story about persisting. Anne Frank documents her life as she writes in her diary, which she has named Kitty. Anne and her family have gone into hiding into the annex at her father's work. Anne is living with not only her parents and sister, Margot, but also a dentist friend and the Van Daan family.
The Van Daan family as a whole is important to Anne. Mr. and Mrs. Van Daan are in some ways the opposites of Anne's own parents, who are normally calm and positive. The Van Daans argue with one another and complain constantly. They have one son, Peter. Peter and Anne grow close throughout the time that they are hidden. Mrs. Van Daan appears to be jealous of their relationship. She does not want to lose the close connection that she has with her son; however, at times, she does take on a maternal role with Anne. Anne is able to confide in her when she feels she cannot talk with her own mother.