Well, it is a surname on an individual basis, but in Iceland you’d say “Thórhildur Sunna Aevarsdóttir” or “Thórhildur Aevarsdóttir” on first mention (as the article did,) and then address her as “Thórhildur” thereafter.
Writing for the English-language readers of the New Statesman who are not familiar with that style, however, that might come off as odd or rudely informal. Think of it as similar to how English generally swaps Japanese given and surnames so they’re in the “correct” order and we don’t go calling Mr. Kurosawa “Mr. Akira.”
