I've been questioning this since that interview, being part of the staff she surely would have known that her school was getting an extra ped day once march break ended, to mention at the last minute, well his sisters were in school so I decided to take him with me is so odd, it should have been planned in advance.
Given how close the school is to their house i really think she was planning on leaving him alone because hey, if he has any problems, he could just come and get her. I think its likely shed just never left him alone before and got cold feet last minute and decided to take him, because it literally makes 0 sense that she wouldnt have known her daughters wouldnt be there to watch him.