Spellfire by Agatha Willow

Bryn swore she would never go back to Grimoire Academy. But when her beloved former Professor passes away and leaves her prize spellbook library to Bryn, she's forced to return.

Bryn isn't planning on staying long, but then she runs into former queen of Grimoire Academy, Amelia Hexford, now headmistress. When Amelia begs Bryn to stay and teach the former professor's classes, Bryn's so flustered by the beautiful witch, that she accidentally agrees to stay for the semester.

Amelia was always too cool for Bryn at school, but now, the staffroom is too small a place to hide in. As the unlikely pair spend more time together, Bryn and Amelia might just find themselves spellbound by something other than magic…