My younger sister takes a lot of things personally. How can I help her get over it?

She is still upset at our older cousin scolding at us for being “RUDE” for not putting in another roll of toilet paper for some when the paper is almost done or out. I told my sister to just don’t worry about it and just move on but our cousin had a point. She is like crying a little bit because she got called rude and scolded off. She is a very sweet girl and she beats herself up when she screws up. I told her that she needs to toughen up and we all screw up sometimes and just got to get over that and move on.