I was surprised that there was nothing else in the book re. Petunia's childhood correspondence with Dumbledore. I also was surprised that apparently some contact remained between the sisters, as Lily refers to baby Harry breaking a vase that Petunia had sent to Lily for Christmas. I had the impression that there was no contact. I also wonder what happened to the Evans parents? Lily was 21 when she died, so they probably were not that old, yet it seems both must have died.
Maybe they died in between when the girls were in school, and when Harry was born? I dunno... maybe that was one of the things to leave open-ended....