Sookie and Jackson have been shown doing nothing but bicker over the quality of his produce since the start of the show. In the conventions of romantic comedy, when two people keep arguing “like an old married couple”, the audience knows they are destined to be together some day.
Sookie is genre-savvy enough to know that the person she has been bickering with must be her romantic destiny: Jackson even acted like a jealous lover when Sookie checked out somebody else’s fruit. She takes immediate action, showing that she really is quite the relationship expert.
Her choice of Jackson is a practical one for another reason: she said she didn’t have time to meet people as she was so busy at the inn, so it makes sense for her to ask out someone she knows through work.
It is notable that while Sookie is always interested in Lorelai’s potential relationships, and gently pushes her toward Luke (her obvious romantic destiny in the show), Lorelai doesn’t reciprocate. She’s never said anything to Sookie except to grumpily tell her that as a long-term single, her opinion on relationships is worthless, and has never given her the tiniest nudge towards Jackson, who they both see nearly every day.