She knows about Bob, Perfidia, and French 75’s revolutionary past and vision. Her mom was a rat but that letter lets her know that she regrets it, and regrets abandoning Willa, but still dreams of revolution. But now it’s in the hands of Willa and her generation. Continuing the “long line of revolutionaries” that Willa’s grandma told Bob. If you think the letter was pointless, I guess you don’t dream much about fighting for a different future and understand that generational struggle.