Cases where a childless woman kidnaps a baby and kills the real mother are actually not so uncommon.
I remember a very gruesome case in Eastern Ohio around 10 years ago.
The murderer befriended a pregnant mother, then one day when she was in an advanced stage of pregnancy, she killed the mother and actually cut the baby out of her womb.
She (the perp) was quite heavy, so her friends and family were only a little surprised when she turned up with a newborn she claimed she had given birth to.
Someone got suspicious, though, and later the police found the dead mother buried underneath the floorboards of a garage, IIRC, and put two and two together.
“Cases where a childless woman kidnaps a baby and kills the real mother are actually not so uncommon.”
She wasn’t childless, she has three children and she is 30 yrs. old. Her oldest is 16, then 10 & 6.