This is no surprise, she ran a good campaign, and her main opponent was rather incoherent in his campaign, and allowed her to paint him as being against abortion rights.
She will be running against Republican state Senator Scott Brown in the general, but she is pretty much in a dead girl/live boy* situation.
*Edwin Edwards, when discovering that he would be facing David Duke in the Louisiana governor’s race, said that the the only way that he would lose were if he were, “caught in bed with a dead girl or a live boy”.