i am sorry to say but she is actually right,, my son was not sleeping for more that a couple of hours when he was 4-5 weeks old, a friend of mine suggested rusks, i was hesitant at first but hey it worked.
i think that instead of getting annoyed with her look upon her as your own mother who only wants to help. i know she does not mean any harm, but at the end of the day it is you baby and you should do what you feel comfortable with. goodluck!