Why Abby says we need Jesus

Isaiah asked Jesus to come into his heart Sunday. I talked to him afterward making sure he understood why we did that as Christ followers. Abby says "We ask Jesus to be our savior and forgive us of our sins so we don't have to kill any guinea pigs" I said what? And she says "well you said before Jesus they sacrificed important animals to pay for sins and in my world that would be guinea pigs"