I try always to give the benefit of the doubt when possible, but I'm with others who have commented on DB's having said she didn't initially check the back yard because she was afraid of what she might find. If there's even the tiniest chance your child might be lying out in the cold - alone, frightened, injured, needing her mommy - your fear of what you might find would never overrule your desire to locate and help your child. It just wouldn't.
That statement is the only thing so far for which I can't conceive of any alternate, benefit-of-the-doubt explanation. I mean, who would choose to let a potentially injured (or at least cold and missing) baby lie in distress in the elements - possibly every second counting for saving her life - because they're too worried about what they might find? No one - especially not the baby's parent.
This is nagging at me more than anything else so far. I'm still not ready to say she did something horrible to her child, but that statement is absolutely ridiculous and was made for a reason - either it was a poor attempt to think quickly in response to being questioned about the back yard (maybe to cover the fact that she knew there was no need to look there) or she knew the baby had been there and didn't want to associate herself with any evidence that might turn up.
I'm hoping I'm overlooking an innocent explanation. If someone can think of one, please post it. I'd love to have a reason not to feel this way about that statement of hers.