mother and lil sis

So...you are the oldest sister and you have little sister name, Lily. Your mom raise you two alone since your father died and after you gratuted, you were working hard. And...you promised your grandparents that you will visit at summer and also promised to your sister. Now...you were in summer vacation, as your promise, you have to drive your mother and sister to the village of grandparents. But you were feeling sick and didn't say anything because you know they will think you were giving reason*