We're The Groupnors

I personally wouldn't worry about it, especially if she's well put together, and the need to wear specific shoes is for medical reasons.

From the Oceania website: "Recommended on board clothing is resort or country club casual. For evening dining, elegant casual resort wear is suggested. We request that casual jeans, shorts, t-shirts, baseball caps, sandals, or tennis shoes not be worn in the restaurants after 6 PM. Baseball caps may be worn in the Terrace Café after 6 PM. " Only "casual jeans" are excluded.

The Oceania website specifically requests "casual jeans" not be worn in the dining room and specialty venues in the evenings. To me, this would indicate that nicer, designer jeans are welcome in the evenings. While I typically wear a dress to dinner my husband will often wear designer jeans with a collared shirt, a blazer, and dress shoes. He always looks great, and in fact looks more put together than some others who are in chinos or slacks.