Mine finds two ways of surviving the fever: the first is in the Temple, they have magical tools to improve crops or improve the taste of wine, but only nobles can use them. However, nobles are becoming scarce in the city Mine lives, as war is making them leave to fight as knights. So, she makes a deal with them to be treated as a noble apprentice in the Temple, using their magical tools and reading their books.
The second discovery is that Trombey seeds (that plant that grows uncontrollably), act as a kind of natural magical device to "eat" the fever. And that's just Volume 3, there is SO much more to come as she grows (in power only, she stays a shortie for a long time xD)