Best gift for cruel prince fan?

My friend's favourite book series is the cruel prince trilogy but she doesn't have the physical copies of the books. So for her birthday I was thinking of getting her the trilogy set. But then I thought maybe it'd be more special to get the collector's edition? But I don't really have room in the budget to get the collectors edition for all 3 books in the trilogy, so I'd probably only get the first book in that case. Then when I was researching I found other books that I suppose are side stories? Like the king of elfhame and the stolen heir? But I might be confused about that so correct me if I'm wrong. I don't believe she's read any of those side stories yet. Anyway I'd really appreciate some advise on what books I should get her ^^