They did. Both
Joachim & Alexandras and
Frederik and Mary's are public.
Except for the names they are prettymuch the same. That was before the change.
As someone has mentioned the Danish Royal Family is rediculesly poor. Especially compared to other royal families. They own almost no propety, Shakenborg ,Marselisborg and
Château de Cayx excluded. The apanage is about 8.6 million euros to the queen, of which she pays 10 % to Henrik and 1.5 % to Princess Benedikte. Out of this she has to pay for her household, interior maitenence on all royal propety, personal staff in royal houses and whatever private needs she has. So as anyone can see, the Royal Family arent exactly swiming in money. And the only one making money is Joachim, though not much.
Prince Joachim almost bankrupted the family twice, once with the weding and again with the divorce. No doubt a potential devorce between the CP couple would be much worse for the family. Not only would it be bigger and more expencive, Frederik also doesnt have anything of real value like personal real estate or a company like Joachim did. So the money would come from the main source, the Royal family. And it could possibly brake it financially, something noone is interested in. So there is no doubt in my mind that Mary was under great pressuere to sign a new pre-nup. Not only from the Royal Family, but perhaps also from other figures inside the government.
The real question is of couse, what has she be promised in return? No doubt some deal has been made. Perhaps a private arrangement with the government or one of the Royal Families benefactors? Or perhaps a promise by the queen herself that she would not stay on the throne for life, but step down within a few years...
No doubt a devorce would be less likely then, and at the very least a devorced queen is better then a devorced princess...
Being the mother of the former CP doesnt give Mary any special deal as such, though im sure the parliament would quickly make sure she got on the civil list...