So I just got the undead thrall spell and I had a question about using it on mages. I was planning on killing Aranea Lenith and using it on her, but I've never had a mage as a companion, so I was wondering that if I gave her a dagger with absorb magicka on it, will she automatically use it or will she wait until she has run out of Magicka to use it? She uses a wide variety of spells, so enchanting her armor to lower costs of a particular type of magic won't be very useful.
Also, can companions/thralls hurt you with their magic attacks? I doubt it, but I'm still curious.
I'm pretty sure she will maintain the same play style she used when you fought her. If she tried to stay away from you and use spells, she should do the same as your pet. If she runs in first to slash at you with a dagger, then she will do that too.
Even if she runs out of magicka in a fight, that doesn't mean she's going to automatically run in and slash because she has knowledge of the enchantment on her dagger allowing her to refill her magicka. I don't think her fight scripting goes that deep.