Like I just said, she's not a very good assassin. She's only in it as a means to make money. Why do you keep thinking this is realistic? If it was realistic, this story wouldn't happen. The whole thing is a romance doujin so excuse me for "over-romanticized" this manga, even though most of my observations are true.
Also thanks for the unfounded advice, I've read a lot of books. You should stop being overthinking it and enjoy the story instead of being a stick in the mud.