1 yr old bb has a round spot on her back, skin surface looks eroded with a darker crust in the middle. area around the crust is wet and expanding?

Possible infection: Your description covers several different conditions. The main thing to consider if it is a new spot, is impetigo, a bacterial infection that needs treatment. Your baby should be seen by a family doctor

? Eczema: However, can't make a diagnosis without examination, kindly see your primary doctor or get referred to a dermatologist, best wishes