A book about a girl who is orphaned and in care of a relative (I think an aunt). I believe they were also heading west on the Oregon Trail, but not 100% about that detail. The relative “sells” her into a marriage with a much older man when she is very young and she goes to live with him on her (once again, I think 15th) birthday. She takes something that belonged to her mother ((blanket or dress?) Her relative doesn’t want to give it up but since the girl does it in front of her new husband, the relative had to give in.  I think the husband dies of a heart attack soon after arriving at their new home.