Are you talking about Varvara Dobroselova? " #'s first novel 'Poor Folk' is written in the form of letters between the 2 main characters ... who are poor second cousins. A deep but odd friendship develops between them until Dobroselova loses her interest in #, and later in communicating with Devushkin after a rich widower Mr. Bykov # to her." https://en.wikipedia.org/wiki/Poor_Folk