Although there are times when we don't get on with our brothers or sisters we should still remember to pray for them. Here are some things that you may want to pray for your sister.
If your sister isn't a Christian then you should ask God to help you and other people to talk to her about Jesus.
If your sister is a Christian then pray that she will become a better and stronger Christian.
Pray for your sister and her school work, any problems she has at school, any exams she will be taking.
Have you had an argument with your sister? If so, you should pray about it. Ask God to help you say sorry and sort things out. Pray that you won't get into arguments in the future.