Found: YA? Epistolary novel, historical fiction

Plot: a young girl writes letters to her neighbor (an old man) who stays cooped up in his house. She talks to him about her mother, since he was friends (or some other relationship) with her. She also talks to him about her brother getting drafted, and he talks about how he protested war back in his day cause he is a quaker.

Complexity: I read it in middle school, so it’s probably around high school reading level.

Cover art: I think I remember the cover having purple, but i’m not sure.

Please help me find it!

That is the book!!!! Thank you so much!!!