Your sister has no reason to be snooping around .. I dont know her age so its hard to figure out what may have prompted her to do this Is she younger is just noisey ?

Here is the thing about Smoking everyone pretty much knows and agrees its really bad for your health ( i am an ex smoker so I understand) I honestly would be really upset if my 22 year old daughter started smoking ..its dangerous and hell expensive but it is her choice. She is an adult .

Give your Dad some time to calm down and then maybe have a talk with him . Maybe he is just scared for you..

There is no point calling yourself a bad person .. buying and smoking cigs does not make you a bad person.