... Connie didn't kill Irwin because he had too much life force? Really? You'd think it would be a banquet for Connie's Hunger Demon and it would want even more. I thought that was the point when Harry fed Lara's Hunger demon, so is Connie now slave to Irwin? ...
Connie was feeding on Irwin's "life-force." He just has a
huge amount of it... more than her Hunger was capable of eating.
Harry was feeding (since Harry kept control, I'd suggest he was force-feeding) Lara's Hunger with
magic: the raw stuff of Creation itself (and, likely, a dusting of Winter (or so says Mab; and if she says it, then she believes it (though she can still be mistaken))).
It's like the difference between a poppy-seed bagel, and heroin.
But... your point isn't entirely wrong, I think.
I don't think Irwin's life-force can "enslave" Connie, precisely; but I suspect something on the habituation-addiction spectrum is at least theoretically possible (fortunately for Connie, Irwin is genuinely a good guy, and unlikely to take advantage if it happens!) .