I think you're all looking at it from the wrong angle. The PPP does not appoint blacks for electoral viability, but for image reasons.
No matter the cries of PPP hatred of Blacks, Western emissaries will still write home about the Black prime minister. That's good enough for the PPP.
Loyal, Black, knows their place, no policy ideas whatsoever. And she is known in foreign diplomatic circles. She is perfectly suited for the PPP's purposes.