in short, during 400 years of Tinaasha live as witch, she only has one regret, this was hinted in previous chapters, her regret is about magical lake, to expalin this I must first explain Tinaasha's origin
Tinaasha was become witch by accident, Tuldar was a country that put more importance in Magic, even their royal throne is not decided by blood, but by magic capability, Tuldar keep children that have magic potential and train them in expectations they will become the strongeat mage and new king/queen. Tinaasha was one of those children, and she was exceptionally good with magic even during her childhood, this make Lanak the real royal prince jealous, at first Lanak was a kind man and nice to Tinaasha, but her inferiority complex toward her drive him mad and he trick Tinaaha to sacrifice her to harvest her magic for himself, by pouring her magic into magical lakes. but Tinaasha's magic was going haywire and exploded, destroyed Tuldar, killed everyone nearby, and gave birth to 5 magical lakes. Tinasha then later become a witch.
Tinaazsa always want to resolve those magical lakes condition, but she can't do anything since she need to know their original names, things that only Lanak tge original creator know. that's why Tinaasha goes along with Lanak 's plan, waiting for him to recite the spell to comtroll the lake so she can know their names and take over the control herself.