Abby may be the most disloyal character I've ever encountered

I'm currently playing for the first time and am in the chapter where she rescues Lev from the island (who went there under his own free will, by the way). As I'm murdering my old friends from the WLF, I'm wondering who would really do this? Nothing against Lev, but you don't start killing your own group because a sweet, troubled kid you just met runs off to find his mother.