My Sisters Softball Coach is terrible?

I can understand your annoyance but my only advice is to help your sister and teach her the right stuff. Then when it comes to her being coached by the bad coach just tell her to ignore what the coach says, however make sure you tell her to be polite! Just have her nod along with the coach and when the coach leaves have her play her game right:) I know it's not the best solution but it's a tough situation and it's the best I got...