Suggestion, you could have it that Princess Frosthair's "palace" is connected to an underground river and/or lake and there is from there they get their water. This makes it a bit more miracle like in a way, a Venice in the desert without any connections to the sea and any other rivers than the once that flow from the city.

And now when I think about it, this idea could also be used if you want to go a bit high-fantasy and have dwarfs, or something like that, living underground and using the underground part of the river/lake. Princess Frosthair's people could be trading with them - spices and other aboveground things for the finest metalworking the world have seen, there is also all the mineral based pigments that underground people probably have.

But this idea probably makes Frosthair's people a bit to economical/political powerful, if they not only have control over a greater oasis and more or less monopole on fish trading but also have better metal items then all the other people

P.S. is Frosthair her real name or a working name? It just sounds strange, for me, with a princess in a southern land to be named after Frost

P.P.S what do you mean with 'fishwife'?