Alice wonders what would have happened if things had gone differently in seventh year. If she hadn't had that stupid fight with Lily about the other girls in their dorm knowing that they slept in the same bed. If Lily hadn't stormed off, frustrated at Alice's concerns at what other people thought. If James Potter hadn't been down by the lake when she arrived, and if Lily hadn't been too upset to snap at him the way she often did when he tried to flirt with her.
She wonders what would have happened if she hadn't found herself sobbing her heart out to Frank Longbottom, who was kind and sweet and gentle and willing to listen and understood that even though she didn't want people gossiping about her, she still cared about Lily.
She wonders what would have happened if she and Lily hadn't kept up the coldness, if Lily hadn't gotten annoyed that Alice had been talking to Frank and if she hadn't gotten annoyed that Lily had been spending time with James.
Because if Lily and James hadn't married, and if she and Frank hadn't, then the prophecy wouldn't have meant anything to any of them. It would be someone else's baby. Someone else's baby with a destiny.
And Lily would still be alive and maybe even still her Lily, and she wouldn't be the wife of a man with a job that she's sure will get him hurt some day, and she wouldn't have to worry that her son might grow up with the weight of the world on his shoulders, and everything would be all right.