I get why your upset, I would be too if someone said that the reason Abby was the target was based on how she looked in comparison to Libby, as a former jock myself there are plenty of guys who love a girl who can kick a soccer ball
my reason for thinking Abby was the target was based on her "look" as a whole and the other missing girls in the surrounding area, making my theory a SK not a random one time attack. IMO Libby just looks like a really bad person to target, she is strong and she would not give up, not saying Abby would but physically she would be easier to control. Hope that helps you to understand at least where my opinion a little more.... they were both very beautiful young ladies.