You can pop the fragment by name. While adding fragments to the back stack, just give them a name.
fragmentTransaction.addToBackStack("fragB");
fragmentTransaction.addToBackStack("fragC");
Then in Fragment_C, pop the back stack using the name ie.. fragB
and include POP_BACK_STACK_INCLUSIVE
someButtonInC.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
FragmentManager fm = getActivity()
.getSupportFragmentManager();
fm.popBackStack ("fragB", FragmentManager.POP_BACK_STACK_INCLUSIVE);
}
});