She wanted me to buy her cigarettes
Why does she want you to buy her cigarettes?
Who cares? She can't smoke in my house anyway.
Smoke is harmful to human health and can cause many problems, but she has a right to smoke and you can't stop her just because you don't like it.
My house and I can do whatever I want.
You have a right to ask her not to smoke in your house, but your tone of voice regarding her smoking comes across as controlling. Don't mistake your rights for what you want and come down on her for smoking.