A 3rd theme in Crime and Punishment: Dunya's intended marriage

In the 3rd chapter of Crime and Punishment Dostoyevski introduces another major theme and plot element, as Raskolnikov, returned to his inhospitable apartment after scoping out the premises of his intended murder victim and listening to the pitiful monologue of Marmelodov, who'd spent all his money on drink while allowing his daughter (Sonya) to support the family thru prostitution,receives a letter from his mother. He hadn't seen his mother (and sister, Dunya) for 3 years, as he supposedly pursued his studies in St. Petersburg.The letter informs him, first, about a scandal that touched on his sister as she was suspected of having an affair w/ the husband/father in the house where she worked as a servant - this accusation made her a pariah in their village, but eventually her name was cleared and the accusing family repented (a foreshadowing of FD's theme of crime and redemption). Central to the plot of C&P, however, is the news that a lawyer, Luzhnov (?), plans to marry sister Dunya. R's mother writes effusively about this man, but we obviously can read through her enthusiasm and recognize that L is a horrible person who will ruin D's life. For ex., the mother praises him for helping pay for their intended journey to St. P - by paying for transport of some of their furniture, leaving them to pick up the rest of the cost: hiring a peasant to take them in a wagon 6 miles to Moscow, then traveling 3rd-class to St. P. This man, 45 years old to Dunya's 18)says he wants a wife with no dowry so that she will e completely dependent on him, and many other disparaging observations, which R's mother brushes aside. She's obviously trying to make the best of a bad situation, but in the process comes off as almost criminally blind to her daughter's predicament and intended sacrifice. We get in this chapter another form of access to R's mind at work, as he obviously can see through his mother's letter and recognize the danger to his sister - and in the first paragraph of chapter 4 he resolves that this marriage is never to be. Amusingly, FD describes the letter as of two full pages; the pages must be the size of a newspaper sheet, as the chapter is about 15 pages long!