The guidelines don't really talk about bilingual literary books, but I would consider them Category 2. Here's the thinking behind that:
The words we can use for Category 1 are anglicized, incidental, and/or occasional use of a non-English language. Anglicized refers to a word like "fiancé" that comes from another language but has been adopted into use in English and isn't really "foreign" anymore. Incidental use is typically where the reader isn't expected to understand or be learning the non-English material. In my mind the opposite of incidental would be meaningful use of the language. "Occasional" is actually from the old version of the guidelines, but I think it's still good to consider whether the language is used throughout the text or just here and there; do we expect the braille reader to encounter the non-UEB symbols enough to remember them?
In a book like this, Spanish is used consistently and meaningfully (not incidentally), so I would treat the Spanish material as Category 2.