if she wanted some lungs back, did it really matter which Vidiian she took them from?
If the Phage could jump species, no one would have been safe.
If an example had been made, a mass execution, maybe Durst and B'Elanna wouldn't have been murdered a couple weeks later.
Actually, considering their problems with the Kazon, why not get those two together? Trick the Vidians into harvesting from the Kazon in a less than a cold war under the radar sly sort of way to start a full scale hot war?
That's totally judo, hardly Starfleet but very smart.