There were no proofs of charging Surjan by Rosie. She acted to Surjan like she wanted to help him because she liked him(or maybe she tried to seduce him so that he finally accepts to sleep with her!) and also wanted to finish the bad things happening around the red light area.
Rosie spent too much time with him and it is also true that she could get her revenge without helping him. But she wanted not only to kill them but also to show the world what they did to her and why did such accidents occur and they deserved death sentence. At last everybody including Surjan came to know what they did. This is what she wanted.
Another point also to be considered that like Frenny told "Dissatisfied souls seek other dissatisfied souls(whether living or dead)". Surjan was in pain, so maybe she thought of helping him as he was in pain due to his sons sudden death. After all till the end of the movie it is evident Surjan started believing in ghosts.