Most probably your baby is suffering from viral gastroenteritis
and during this period children do suffer from transient lactose intolerance
.Restrict her milk intake and instead give her yogurt and probiotic
.See to it that she is kept well hydrated with oral rehydration solution if the frequency of motion go high.For the rash you could apply calamine
lotion.If she starts getting fever or if her urine output becomes inadequate and she eats poorly then get her examined by her docter.