I don't understand what is she sacrificing herself for ?

I believe she is sacrificing herself for the dukes people, not the duke or anyone in that house. She is worried for the people trying to get food without proper equipment or really, any financial support to help the kingdom thrive.
(Let me know if I'm wrong but thats how I took it)

By reading your answer I remembered her talking of peoples lives in this fiefdom being difficult. You right