Say something or leave it alone? ??advice wanted

My sister informed me that my our oldest sister is going around sayimg that I am sleeping with our father. I dont get along with her. I have always been there when neeeded me. I am sick if evil ways so I cut out my life (hurts miss my nieces n nephew). I am very angry and mainly because it hurts mean this is my sister . She always had issues with our father being close to me . I didn't meet him or her till highschool. She hated how he took to me even though am lesbian. Told him that im am going hell . Mind you has there beautiful kids out wedlock three abortions and one late miscarriage. My dad says it okay leave it alone die out. However I am sick of her . Should I call her or let it go???