Trix is pleased that both Lorelai and Rory are taller than average, and after quizzing them on their health, glad to hear they are strong and healthy. She tells them that they must have a majority of “Gilmore blood”, as Gilmores simply never get sick. This must be why Lorelai and Rory remain healthy in spite of their junk food-loving lifestyle – they truly hit the genetic jackpot.
At the time, it doesn’t make much sense that Trix should be so mad keen on “Gilmore blood”, as it was her husband who was a Gilmore. In a later season, we learn that Trix married a distant relative, and she was born a Gilmore as well.
The Annotated Gilmore Girls 