Is there other form of sibling attraction besides GSA?

I have read about GSA and learned that attraction between siblings who didn't grow up together can occur.. But is it also possible for such attraction to happen between siblings who did grow up together. Not really sexual but is it possible for a younger sister to actually like or fall in love with her brother even if they grew up together. I have learned about the Westermarck effect - and I actually have the sense of feeling of being disgusted when I think about it - so I don't know if that thing could happen. I'm asking because I'm trying to evaluate my friend. Thanks!

Evaluate your friend?

I think the answer to almost any question involving people sooner or later is "yes, that is possible." Almost nothing about us is so set in stone it could NEVER happen.