C.T.
It's possible she had a tummy ache as a result of drinking milk or it didnt taste right etc. Maybe she's developing some lactose intolerance. Kids are quick to make associations like that and they tend to be lasting ones. My 4.5 yo son decided he didnt like milk at all - it happened around 2. He will drink a little here and there but we don't push it. Thankfully he will eat other dairy just not milk.
If you give her plenty of calcium and Vit D rich foods, she will still be healthy even w/o drinking milk.