Unfortunately, a DA has the right to call his cases as he sees them. He's the only one who can decide whether to prosecute a case and in what manner. He will also decide the plea offer, if any. Although a DA will certainly listen to the concerns of his victim, he is not required to do what the victim wants.
There is an office review process, and if you feel the particular assistant is not doing all he ought, you can take the matter up with his supervisor and as far up as the DA hinself. But if the DA looks the matter over and believes the way the assistant is proceeding is fair, that's how it will go. And there is nobody over the DA himself who can make him say or do otherwise. Having already done this, you cannot change the DA.
If you feel that the DA's Office is doing this because they are corrupt, are committting misconduct, or that there's a conflict of interest makes them pro defense, then you could complain to both the Pennsylvania Bar.that would change the fact patterns. You could file a complaint against the DA with the Pennsylvania Disciplinary Board
of the Supreme Court of Pennsylvania, file another one with the State Attorney General and even, if you feel this is so egregious that the Prosecutor's Office is abusing their authority, you can even contact the FBI.