I'll start with I play on PC and I don't use any mods. I started a new character for the event, a single female living in Willow Creek. I was able to do the event through the planting of the flowers ...
Ideas
I'm having this issue too, the newsletter is just not being delivered. I also play a completely Vanilla game., never used mods or CC.
What kind of residential lot are you playing on ? Have you tried replacing the mailbox ?