Your girlfriend is suffering from a postpartum mental illness - you need to speak with her doctors. Some women can suffer crippling anxiety or OCD in the postpartum period, akin to postpartum depression of postpartum psychosis. She needs help.
As for validation - it’s not about not defending yourself. It’s about hearing what your daughter is telling you and acknowledging her feelings. You have to get out of your defensive posture to do that.
You can validate without acknowledging wrongdoing.
