Answer: the hormone is Oxytocin
Explanation:Scientists have found clue to the hormone responsible for maternal instinct which is "Oxytocin". Oxytocin is also called the love hormone which has been discovered as very important in maternal behaviour especially in nurturing and protecting the baby.
It was discovered that postpartum women with consistent high levels of oxytocin following childbirth displayed bonding and care as well as overcame their reservations about not knowing what to do as a mother, compared to women who had decreasing levels of oxytocin.
Scientists have linked the release of oxytocin to the activation of cells in the brain which are believed to stimulate maternal behaviour in women, which is what Jackie experienced and how she became "in sync" with her baby.