Here are 2 Bible verses about loving your sister from the Old and New Testaments of the Holy Bible (King James Version), sorted from most to least relevant.
John 15:12 KJV
This is my commandment, That ye love one another, as I have loved you.
John 15:22 KJV
If I had not come and spoken unto them, they had not had sin: but now they have no cloke for their sin.