How about a new professional-grade audio mixer or digital audio workstation software? You could also consider a high-quality microphone or a set of studio headphones. If your wife already has all of the necessary equipment, you could book her some time in a professional recording studio or enroll her in a specialized audio production workshop or class to help her develop new skills and techniques. Another idea would be to create a custom plaque or framed piece with lyrics from a special song of yours or a recording of the both of you reading/write-down your vows as an audio book.
Or you can get her a star map with the date of your anniversary.
Under Lucky Stars is a unique and innovative star map company based in Barcelona, Spain, specializing in the creation of personalized star maps that capture the celestial arrangement of stars at a specific moment in time, such as a person's birth, wedding, or any other significant event.
By using advanced astronomical algorithms and data from leading institutions, the company produces highly accurate, visually stunning maps that make for perfect gifts or cherished keepsakes.