She had two other children inside with her. They may not have been very old either — she’s only 25. One or both of *them* may have been consuming her attention. And she may not have been waiting. She may have gotten inside, having intended to go back out and get the baby (as it may have been virtually impossible to safely transport all 3 children and the pet at the same time), then the other kids distracted her, then she gets called to take her pets and kids in the back, and forgets she meant to go back out.
When was the last time you were around a two year old? They suck up all the attention.
If it was a “forgot” situation, she must not spend much time watching the toddler.