Ianthe and the Realm of Magic

Ianthe never believed in spells, or curses, or enchanted elixirs. Her sister, Maeve, on the other hand, revered in the possibility of magic and was even convinced that their mother was a witch! When Maeve finds the door to their mother's secret room unlocked, she discovers a lair -a witch's lair-behind it. Still skeptical, Ianthe doesn't believe the room proves anything. But after Maeve reveals pamphlet featuring a magical school, Ianthe finds herself following her sister on her quest to find it. Coming upon a portal hidden in an old oak tree, she crosses in a new world full of magic and mythical beings. Though reluctant at first, Ianthe decides to attend the school with her sister-perhaps she could learn a spell that'll keep her plants alive. And if her mother did go to this school at some point, maybe she could shed light of her sudden disappearance and the secrets she's been hiding.

I'm just using this cover until I come up with something better.