I dont remember much from the novel but......
I think she is just a regressor not a transmigrator. She thought the body she was in was not her own(because of the bet she made with the witch) and thinks she read the life of Sheriel in a book when in fact it was actually her future. The one she went back from. From what i remember, sheriel met the witch when everything was burning up in flames(kardicel became the ultimate villain, trying to kill both his parents and Kian, saving sheriel from it, dies) thats why sheriel had a chance to meet the witch and she asked to see her mother and the bet with the witch that if sheriel was telling the truth(that she only loved her mother and no one else) she will give sheriel a better life (transfer her to another world without her memories) but if she was lying she will stay in that body and be miserable, reliving her sad life all over again. I think in the end she chose to stay in the past and be miserable(remembering her dead mom and the life they both live through) but is loved and she now accepts their love despite everything.
......... I might be wrong tho, i only remember some parts from the novel.

So she transmigrated in the beginning, right? That’s how she was able to read a novel about that world… but somehow this turned into her going back in time ten years? I’m so confused. So if I find a witch and go back in time ten years (as an adult) this will cause me to transmigrate? Someone spell this out for me. I’m lost.