I want to fuck my aunt,how do I tell her?

I am almost 15 and she is 37.We live togheter and she doesn't have husband nor children.She has sexy ass and nice tits.I saw her boobs once and she knows that.I walked in my underwear in front of her and she looked at my dick.She doesn't go to parties and I am sure she doesn't have sex for a long time.Please help,how do I tell her??