RORY: It’s tradition.
DEAN: I don’t believe this.
RORY: It’s true. My mother and I have been doing this every year since we moved here.
We now know that Lorelai has been taking part in the Bid-a-Basket Fundraiser since 1987, even though she was a maid at the inn at the time, and had only been in Stars Hollow for a few months. It seems she became heavily involved in the town almost immediately.
Rory says she has also been taking part since she arrived in town too, but she was only a toddler. Perhaps she means that she accompanied Lorelai on her picnic lunch dates, as a sort of chaperone to make sure things could never get too romantic, and because Lorelai either didn’t want to leave her with a babysitter, or had no babysitting options.
It’s unclear at what age Rory was deemed old enough to take part in the fundraiser with her own basket, but most likely not until she was sixteen and had a boyfriend to buy her basket. That would be since the previous year, 2001. So Rory’s grand “tradition” has probably been going for a whole twelve months.
It’s also “tradition” for the woman to bake a delicious picnic lunch, but Lorelai and Rory don’t bother sticking to that tradition. There’s so many places that Dean could poke holes in Rory’s narrative or call her out, but he never does.