Take a look at this:
2nd Edition Codex: Sisters of Battle page 34
So the only person in the Ecclesiarchy with any authority over the Adepta Sororitas is the Ecclesiarch himself. This made me happy when i first saw it.
That doesn't mean a Sister wouldn't seriously consider whatever a Cardinal has to say, as they are a man of the Emperor, and they speak His will (well, the good ones do).
Edit: I'm going to go back to assembling that Rhino as an Immolator (since GW apparently can't be bothered to cast that one clear plastic dome, so they discontinued the kit), but I'll keep an eye on this thread.
Edited by Servant of Dante