I understand your concern. This is not ideal and someone has to be with the baby when he is feeding. I would avoid accusing statements and use "I" statements to get your point across. Such as I really think you should stay with the baby because he had wet clothes on and did not seem safe with this situation. Find a compromise and things could change drastically. If you have less stress at work, offer to feed him at certain times and then return to the schedule you have now when your schedule changes. Of course this is an example and you should make your own. This called by resolved with compromise but she has to be on board.
You aren't overreacting. When you come at her with anger nothing will be resolved. You have to talk about this as a couple so you both win.