It could be due to to mental trauma.
Sometimes women with really high libido are also those who have had been abused in childhood. The reason for this is she may be fearful of staying with one man and feels safer with being with different men.
Sometime to much adrenaline can leads lead to high libido as well.
There are many things that can lower a sex drive for women as well. This includes giving birth, breast feeding, and tending to the child. The women will no doubt be more focused on tending to her child.
For women, sex is more mental then men, where it is more physical. So a woman will need to be in the right place in her mind to want to have sex. There are some over the counter supplement to enhance women libido available as well.