Personally, I think she's lying.

She knew the weight (it's on the box) of the box, but why would she put 5.lb on an empty box and pay more? Rationality and Logic would have her placing at least the exact weight of the box to be shipped. Her posts don't show her stupid enough, or absent-minded enough NOT to simply look at the box for the weight... if the box was not empty, there was no reason to "guess" or let USPS catch the exact weight later.
Further, there is not enough evidence in those pictures to even show that those are the correct animals, and this is NOT a bone of contention since the OP is willing to accept them back if they are incorrect.
The ONLY thing that needs to be proved is that she did NOT ship an empty box/Jerome did not receive an empty box
(and that she's who she says she is). Which, by her postings she doesn't appear to be stupid, so it would make no sense if she was shipping the full box, not to put that weight that was noted on the box on the shipping label created.
Right on the first page of the "Pick up Scheduler" (she scheduled a pick up first), there's a place to put the "estimated" weight of the box...why would she put ONE lb when she had the box right there with her and it was not empty?
Her excuses do not ring true, to me.