WMG / I Capture the Castle

Rose was really doing it all for Cassandra.

Rose was desperate to marry into money to help her entire family, but in particular Cassandra, whom she saw as doomed to remain in the same state Rose herself had been. Mortmain might or might not have ever written another book to save himself from poverty (and in any case, he would still have his royalties, meager though they were), while Topaz would either happily live alongside him until Doom or, at worst, get sick of it and return to London and her artist friends. Thomas was smart enough to get from scholarship to scholarship until he graduated and found a job to support himself. And Stephen had already found paying work, and in any case was not a member of the family. Cassandra might have easily been stuck in the castle with no job or marriage prospects, loyally supporting her father, until it was far too late for her to make something of herself. Since Cassandra was too earnest and romantic to ever come up with such a cold-blooded scheme for herself, Rose was prepared to sacrifice herself to a loveless marriage to insure Cassandra's future.