The meal pre-order opens up around 10-7 days before departure, unfortunate the allergen info is a bit hit or miss from outstations but you at least get a guidance by just reading the description of the different meal.

I ended up ordering a GFML [Gluten free special meal], at SAS the GFML is also lactose free but if your wife can handle cheese you can always ask for that during the dessert service.