And Serana herself is just bits of code.

See, I know this and yet she still made me feel like a piece of shit.

There's (what I assume is) a glitch in a certain area. You lure a priest into a basement to sacrifice him to molag bal. If you take serana there, she will cower on the altar, like the priest does just before he is sacrificed. Maybe it's just an automatic thing for followers to facilitate the quest, but I had her with me and holy shit. Considering her history it's especially fucked up.