Calculating Mathilde's net worth is complicated by the fact that a lot of her stuff is priceless. The sort of priceless where money cannot buy it, but if it could you could buy a reasonably sized nation for the same amount.
Runic masterpieces from the hand of Kragg the Grim. A College magic item so potent that it must be integrated into her body so it cannot fall into enemy hands. A personalized sacred relic. A mountaintop home that, even without the semi-divine superweapon, required legend levels of good will to build. A forest city home that stands in flagrant defiance of the laws and traditions governing said city. A library featuring books dating back to the time of the Old Ones. One of the most impactful prisoners since Nagash bagged a talkative Druchii. Temporarily a set of Orbs that the Colleges would gladly go to war over.
Mathilde would likely top 100, if not top 10, if her bling was counted.
While all those are absurdly valuable, (Except the integrated college item, that one can be produced which means it has a price, its just military technology, so its just about as valuable as, say, a modern tank would be, very valuable but not even close to absurdly valuable) none are worth a decently sized nation, unless we are counting the Border Princes. Maybe the superweapon, but that one technically belongs to K8P.
Kragg had made other masterpieces, and while many people would give their left arm for it, I doubt a Tilean Prince would give their country.
Mathilde is not the first nor last person to get a personalised sacred relic from a god. Hers is good, but not really worth a nation, even if it would work for everybody else.
The mountainhop home and forest city home are indeed unique, but very, very much not as valuable as a nation, think of it this way, would you trade the poorest nation (that is not a micronation) of the world for a super villa in the richest?
Mathilde's library is not the only super library, and even if it is the best (I won't lie its in contention right now), it is not worth a nation.
Qurech isn't even valuable, his info is, and his info were not extracted because Qurech was Qurech, but because Mathilde was Mathilde. Queekish, however, is not valuable to anyone who does NOT have a nation, so selling a nation for it would not work. Maybe part of one, admitedly.
The Orbs are, again, not something worth a nation. Rather, they are like nukes, something worth a lot TO a nation.
Mind you, most of these are worth a border princedom or a noble title higher than the one she has or more money than we ever had since the start of this quest or maybe a city burgher lord style, were she to exchange them. But decently sized nation is overly optimistic, for all their pricelessness they wouldn't even be able to buy Marienburg.
Now the patent for manufacturing Waystones COULD actually be worth that much, but we are not the sole owner of that and never could have been.