If this were a book entirely in English and you encountered an accented letter in someone's name, you would use the dot 4 accent indicator because accented letters don't occur in English in the same way as in other languages. English does not have accented letters. In Spanish you have encountered an accented letter that does not occur in that language, so you do the same thing. Use the dot 4 accent indicator preceding that u and list this as a regular special symbol (not as part of the Spanish accented letters). Do the same whenever you encounter an accented letter that does not occur in the language you are working in, whether it's English or some other language.
Hope that helps.