She has a sixth sense.
How could a friend lie to somebody as sweet as Abby? It's disappointing, of course, but the world isn't perfect. Neither is Janice!
Although Janice seemed like a harmless victim, Abby saw right through her and realized that she was actually in on the crime. As the other offenders were being arrested, Abby connected the dots and dutifully turned her over for her role in the hostage fiasco.