I'm not even sure if this book even exists or I have dreamed it. It's about a girl, I remember she had an older brother that went somewhere (war I think) once he reached a certain age. The oldest one died, and the birthday of the the middle one was just around the corner, so he was the next one to go.
I do remember they were really poor and lived in a somewhat caste society or there is some hierarchy. One day mom sent her into the city to do some work (tailoring?) but she had also some plans there so she tried to hide from guards. When she started to get out of the city some rebels made chaos, she almost got caught.