This mod seems to confirm that Karlach is a class not available in EA yet. Paladin, maybe?
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There's a significant lack of voiced dialog, and you may often see |Karlach comment!|.
Looks like Karlach is still very much in development, more so than the other 5 origin characters.
I am pretty sure she's a Paladin. Even if she was forced to, she fought a holy war as a champion. And she says she's very good at killing demons and she enjoys it.