Lucca
Bonding refers to the creation of a healthy attachment between parent and child. For many women, this isn't necessarily an instinctive process, and that can happen for many reasons. The birth may have been difficult. Maybe the baby wasn't the gender she wanted, or has some issues. Not to mention that she has to completely adapt her thinking now. Tilda Shalof wrote in her book, "A Nurse's Story", of when her first son was born: "He was mine, but he was a stranger, and I didn't know if I liked him yet!"
There has actually been a fair amount of research done on bonding, how it works, and the importance of it. If children don't develop a strong bond with their primary caregiver, they can develop something called reactive attachment disorder, or RAD. Sometimes this is observed in children who have been neglected or abused.
When I teach maternity nursing, there is actually an entire topic on postpartum family adjustment.