Technically, she tried to say she took the selfie when they returned that afternoon and that the timestamp would prove that, but everyone speculated that she actually took the selfie before they left that morning (since we don't have any proof of him coming back with her later).
Here's what she said:
and shopping on Monday ( cleared as well for him getting out of the other side). Please don’t think for a second that there isn’t enough of technology to determine shadows and movement around the truck. There was also proof from my phone that we had taken a selfie in the truck in our driveway that was time stamped. We always send pictures to Albert when we are out and about or when he is away. That can be scanned for actual time verification.
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You're right, she didn't actually come right out and say the selfie was taken when they returned, but the implication is there (in the sentence immediately preceding the one about the selfie), when she refers to the speculation that shadows around the truck prove that Gannon came back with her that afternoon.