A question

That's a valid question and you've basically got it right. In the book she was the naive product of a sheltered convent education and was influenced by the romantic novels that she and her classmates read and adored -- castles, dungeons, princes in disguise, and the like. Her mother was dead and she lived on her father's farm, where she pretty much spent all day reading and playing dress-up. She first meets Charles when he was tending the injured leg of her father, so he's somewhat in the position of a "rescuer," and Emma would like to be rescued from life on a farm, even though she never seemed to have lifted a finger doing any farm work. Marriage was the ultimate goal for a woman at that time and in Emma's mind once she was married everything would fall into place and she would achieve a state of constant passion, adventure, ecstasy, and spiritual bliss. The reality of being married to a preoccupied and not especially bright small-town doctor (back then doctors were about as prestigious as barbers) completely shattered her illusions about what the rest of her life was going to look like. And yes, she also was selfish, a terrible mother (in the book she had a daughter whom she abused and neglected), and a clingy, demanding mistress. She never thought in terms of how her actions would affect anyone in her life. And in the end she just wanted to escape.