What was the sin offering for in Leviticus 12:6?

Answer From The Annual Reading Schedule - Week 25 Notes For Leviticus: Verse 7 states that atonement is made for her and she is cleansed from the flow of her blood. But what sin did she do? All she did was give birth right? Isn't it a commandment to bear fruit and increase? Where is the sin? This reminds me of Psalms 51:5. It also makes me think that perhaps our understanding of "sin" is not exactly correct or that there is something deeper here to think about. I don't ultimately know for certain what the sin is, but I will share my thoughts.

This makes me think of Genesis where the woman was told her conception would be increased (Genesis 3:16). I do see at the end in Leviticus 12:8, the end result after atonement is being made clean. Why is the blood seeming to cause her to be unclean? Perhaps childbirth would otherwise have been without the blood if we were never kicked out of the Garden in Genesis? Is the blood due to the fall of man? It does say "atonement was made for her", so is this all somehow related to some kind of inherent sin that exists simply because we are imperfect and have fallen short of the esteem of Elohiym? Or is this somehow related to the fact that the flesh is corrupted and flesh and blood cannot inherit the kingdom of Elohiym (1 Corinthians 15:50)? I do not know.