In the book and the show, Sansa is betrothed to Joffrey, but quickly passed along to Tyrion after Ned's 'treason' and the emergence of Margaery Tyrell. However, things go too far in the original plot for Sansa as she ends up marrying Joff, and even giving birth to his child. Martin's concept for Sansa was that she 'will choose her husband and child over her parents and siblings, a choice she will later bitterly rue'. Thankfully for the young Stark, she managed to flee Joff's clutches in the final product.