Hi, Welcome to Health care magic forum.
As you describe,it appears to be the
lactose intolerance, means the
allergy to the milk, either mothers milk, or animal milk, due to the lactose in the milk.
She must be fed with the soya milk products, which is devoid of the lactose. It can be given for any length of time, till she is taking the routine food like rice, wheat products etc.In a span of time it usually changed.
I advise you to
consult a pediatrician for diagnosis . She may need to get the examination of stools for reducing substances, positive suggests the lactose intolerance.
I usually prescribe to my patient with such symptoms enzymes, lactic acid bacilli, and advise to give, soya milk, till she wants milk.
Wishing for a quick and complete recovery. Thank you.