Brenda could very well be Red John, because she is firstly a news reporter and no one keeps tabs on her. Secondly, how come she is still alive..... Why hasn't Red John killed her?

It is also easy for her to get accomplices, because of the fact that she knows so many people outside and inside the CBI. She is also the most informed person; which means that she knows everything that is happening, hence making it easier to plot a murder (if she is Red John). Who else could hack into CBI? Besides, she has seen a lot of murders herself, so WHY CAN'T SHE KILL ON HER OWN?

She could have very well killed the REAL RED JOHN and carried on the legacy!!