S.H.
Try a straw cup. Those Toddler cups, with a cover that you can use a straw with.
But, for a child "milk" comes from a "nipple." Hence, they like to drink milk from something with a nipple. Be that a breast or a bottle. It is instinct... and to a certain degree, it is comforting etc.
So that is why, many times, they reject drinking milk from a sippy etc.
One day she will drink milk from a cup or straw cup.
My son, was resistant to drink milk from a cup/sippy, but then one day, he would drink it from a straw cup.