Dress codes consist of dressing appropriately for the event you are attending, depending on the nature of the event and the time or place where it is held or the people you are going to meet with.
Wear bright colors, big hats and flashy jewelry to visit refugees, but wear a pantsuit and be disheveled to receive a Head of State... there is no coherence.
Elizabeth II belonged to another era and continued to use the same dress codes throughout her life, but the younger generations have been modifying it and that modification was completed when she died. The most formal looks, the hats, the important jewelry... have been left for the most formal events, state visits, military events... while at other events they dress more in line with the type of event and the people they are going to share it with. Nowadays I can't imagine the Princess of Wales visiting a refugee association dressed like she goes to Ascot.
The same could be said about Queen Mathilde and Queen Mary, who when they started out as princesses were always dressed more formally and have been evolving and adapting their dress codes to the events they hold.
If you look at all the clothes that Máxima has worn this week, there is no coherence... it seems that she dresses as she feels like that day without taking into account the type of event. Today at a fun event with children she wears a more relaxed dress code, but much darker than previous days.