Should Grandparents have visitation rights to their grandchildren?

My sister is involved in a court battle right now with her 4 year old daughter’s biological grandmother. My niece’s bio dad is in jail for sexual acts with a minor, and she has never met him. She also does not know her bio grandma. My sister is married to a wonderful man who loves my niece as if she is his own. In the state of NY, grandparents have the legal right to sue for visitation, and so she has decided to go for it. Just because it is legal, is it okay? It is disrupting her life, and the woman has a past history of depression and suicide. My sister does not trust this woman, and the way the trial is going, it seems she may actually have a chance of winning…