I think it was explained a chapter or two ago. She probably very much expected them (or at least Benjamin, as she acknowledged how antsy he’d be in chapter 1 or so) to basically follow her all the way there if she gave any indication of leaving. Considering how much they care about her and no one else there and their general personalities and protectiveness, they’d probably do something to ruin her plans (unintentionally). It’d be like setting off a grenade in a china shop. Its also because she knows they’d involve themselves regardless of if she doesnt want them to
Also i think its probably her guilt about how bad the ending of that book was and how she feels she caused it. The mages likely weren’t really present in the book and shes probably worried of exposing characters she cared for for years (who would likely be unaffected by the story’s bloodshed and chaos) to something dangerous
It's been a long time since I enjoyed reading a manhua without getting mad at logic, characters, grape...etc. The art is pretty as well, no glaringly wrong anatomical mistakes. Uh.. the only thing I can't figure out is why she left her pupils without a farewell but I hope there's a good explanation. If not oh well another ruined one. (Ch.44)