Ginny knowing Jason

I assume she was from the area with how she talked about him

Did they every say that in the movie?

Paul knew too but was very dismissive of him

It's possible she was from the area, but she may have also been using her child psychology education after hearing the legend. She came on Jason's shack but didn't know who it belonged to. Of course, she seemed very sympathetic to how shoe theorized Jason growing up.