So I was out with a group of friends the other night. One of the girls in this group is an HB8 who I'm not great friends with but we always have fun together and we have hung out together in groups several times. I've never really looked at her as game material. I was hanging out flirting with her lightly and just having a good time. Before I knew it, her friend was telling me how i should hook up with her because she liked me. We ended up doing almost everything that night.

How does this happen? I feel like I barely had to try! Does this mean she likes me or is she interested?

I think you answered your own question in your post. Obviously she likes you, her friend told you. That is a big fuckin green light!