Janette Oke 
When Calls the Heart (Canadian West Book #1) 

Nothing in her cultured East Coast upbringing prepared Elizabeth for a teaching position on the Canadian frontier. Yet, despite the constant hardships, she loves the children in her care. Determined to do the best job she can and fighting to survive the harsh land, Elizabeth is surprised to find her heart softening towards a certain member of the Royal Canadian Mounted Police. Book 1 of the bestselling Canadian West series.