I'm not a Winchester

Danny is 28 when she meets 26 year old Sam and 30 year old Dean Winchester. Being a female hunter, she knows she'll have to prove herself to them. What she isn't prepared for, is when Dean starts flirting with her. She can't stand it, despite having feelings of her own for her partner. They keep trying to protect her, ignoring the fact that she's hunted for years. And act like she's in more danger than them for some reason. Why did Bobby send her with them?