The Lake of Dead Languages by Carol Goodman

Jane Hudson never thought she would return to Heart Lake. Her years there as a scholarship girl ended in a double tragedy: the drownings of her two roommates. Now she is back, struggling to adjust to her new life teaching Latin and as a single mother. But the events that haunted her memories for so many years begin to recur in front of her eyes. It seems she alone can see what is happening, and only she will be able to prevent a second catastrophe…

Surrounded by the lake that gives the school its name, steeped in history and overflowing with the emotions of teenage girls, Heart Lake guards its past – but cannot keep it hidden.