DY: from the article I read it seemed like it was intentional. She had another two kids with her and did some shopping. When she got back to her car she immediately asked where her baby was. She was likely stressed out and the baby was sleeping at the time so she did something extremely stupid and dangerous.
Cases of Forgotten Baby Syndrome usually involve changes in routine which on the surface this doesn’t appear to be the case here, but I truly hope I’m wrong.