I can sympathise I have an almost 18 year old also just finishing A level and living at home with a huge bedroom all to herself. Teenage girls are pretty selfish generally - I know mine are good kids but wouldn’t think to volounteer to clean up or put some laundry away unless I ask! My dd brings her boyfriend round for tea several times a week and they raid the freezer cooking pizza and salmon and drinking all the pop! They just don’t think about others on the house it’s off thier radar. It’s something I think they just go through to push the boundaries with us as parents. I don’t think she’s a bad kid for saying that about your relative just being a normal selfish teen. Hopefully she’s had a think about what you said and feels bad x