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 moved houses and it finally worked have you tried moving? I don't cheat so I was just working my way through the options as they came about, and this one worked for me.
I tried moving and made a new sim and new save and a bunch of stuff but no luck :(