There is a possibility that she has lactose intolerance, but very difficult to give a diagnosis till proven by an allergy expert.
Next Steps
My advice is to continue for zerolac or nusobee for a while and get her reassessed by allergy and immunology expert who could confirm her milk allergy by skin tests and decide if complete refraining lactose in breast or cow's milk and milk products in the future is needed or not in the first place.
Health Tips
I hope this helps