Remember this story?

Hi everyone,
I'm quite new here and hope I'm posting this question in the right place. If not, my apologies.
Do you remember the title of a bdsm Story from the library where an American college girl hired by her aunt to take care of her 2 teenage daughters in their farm was captured and enslaved by her younger cousins at the absence of their mom? After the aunt returned, she offered the college girl a choice between freedom or remaining their sex slave for the rest of the summer, and she chose to remain only to find out her own mom and other aunt were into bdsm too. The next summer she went on to be hired by as a sex slave also by several other people in order to earn money and discover more about her sexuality. At one point she and her mom were voluntarily sex slave sisters at the hands of a mature couple.
Could you please help me with the story title?
Many thanks in advance.