I don't know. I've not tried it with them, but do it on a thalmor soldier from the Thalmor Embassy (heard they cap out at level 36? I'm 69, so they'd be at the cap I guess.)
She is lots of fun. I killed her at home, then smithed her glass armor to legendary and enchanted it for bow and one hand where I could. Then I tossed
her a legendary daedric bow, shield and one hand sword; She goes to town now. You stuff all the junk back in her body, cast dead thrall again and its on.
I love going back to the embassy with her, and Mjoll (my regular follower gal), then killing her own thalmor buddies again.
It just might not work on regular guards.
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Also, not sure on this, but:
I had that daedric sword enchanted for absorb life, 28, or something. I just assumed that it would not work anymore for her
(since they can't recharge it.) When she fights stuff, she always has that "red blood" light thing, like it is svcking their life too.
Do the npcs not need to recharge stuff? It was empty when I gave it to her, but she always has that red blood/absorb life thing.