What would you do?

Am I overreacting? I share custody of my 12 yo daughter with her dad and she just came back after spending 2 weeks over there. We were just talking and she tells me that her “stepmom” dropped her off at Walmart by herself and left her grocery shopping while she went to get pizza. Ummm that kinda pissed me off that she would leave my 12 year old daughter alone, but am I overreacting?