Disclaimer: I Do Not Own CSI.
She was his daughter, it didn't matter that he wasn't her real father.
He still loved her. She had never believed it, and maybe if she had she wouldn't be what she is.
He's tried to save her in the past, but she didn't want to be saved then. He doesn't really believe after everything she's done she wants to be saved now.
But that he'll still try because he's her dad, and he will forever try to save her.