If she was an HE pitcher before then you are working on changing her old muscle memory. Try alternating with and without a ball. Also, many times the changeover from HE to IR is slow not because of what she does with her arm but because of how she uses her body. Closing or squaring up the shoulders is integral to HE, staying open is important in IR. Focusing on staying open may help her transition. Sometimes telling them to stay open doesn't get it done, I often end up having to tell them 'to stay sideways' , that often works better. If she can stay sideways when her arm comes down the backside she is more likely to have her arm in a better position to IR it.