I could see her having issues with Templars in general; I'm curious why you think it'd be about the lyrium addiction itself.
I'm fascinated with the implications of lyrium addiction and want to hear what others think. 
While I think she'll be generally 'pro-mage', I think Sera would be equally appalled at the mages behaviour from what we've seen in Redcliffe.
As for lyrium addiction, I think it's a bit of a necessary evil. If some psychopath mage threatens someone else, it's vital to have some sort of anti-magic abilities. And once it's started, it's best to keep with it. Especially for Cullen, I think.