“..but how did she know for sure the child was dead, unless she killed her herself?”
Casey did not testify, so we don’t know anything from her directly.
“Who says?”
Logic says.
“What physical evidence?”
Exactly, a guilty person will leave some type of physical evidence, and there was none.
As I said above, the job of a defense attorney is to place doubt in the minds of the jury. Casey did not perjure herself on the stand; her attorney did a good job and she was found not guilty. Yes, Casey did not act like a Bas Yisroel, but she was not on trial for that.