Either she was too arrogant to think she'd mess this up or it never occurred to Miss Einstein that covering your tracks would include turning off the date stamp "just in case."
I can turn mine off so I presume it is an option on most digital cameras.
Ive tended to think JA had every intention of keeping the pics. I don't think she meant to wash the camera with the card in it. She knows damn well what a memory card is and where it is on a camera. I also think that the entire reason why JA's original plan didn't work it is because she underestimated how long it would take for him to die and she didn't expect the gigantic mess. Those things made her have to hurry more.