Did you try resurrecting more creatures and casting Aura of Command on them? You are only suppose to be able to have up to the level of that skill following you, so casting it on additional resurrected creatures should hopefully bump Iona's pet off the group following you.
Maybe if you learn Banish, it will work better than using it from an item bonus? It shouldn't make any difference, but it couldn't hurt to save and try it. If it works, you can use
iZakaroN's SaveEditor (or from
Kiya's site, with description) to remove the skill point you put into it, otherwise you can just reload.
