Is tough love good to give to a best friend?

I don't want to be all soft on her when she screws up and being manipulated. There's this girl that she trusts but she is manipulating her and my best friend is too clueless to see that. She yelled at me because she thinks I'm jealous of their friendship? Being jealous of a manipulating person that's ruining her life. I tried to tell her but she is being stubborn!