Friend over, and if she gets hurt. shes 18.?

So my parents are a bit hesitant to let my best friend over because they're afraid that they think she will get hurt or something bad will happen to her over here. My friend is 18. Let's say she doesn't get hurt at my house or property, but she goes out with a biker friend, and she gets injured while riding. She is presonsible for herself right? Legally, no one can blame my parents or I, correct?