True Grit (2010) question

This is one of my favorite westerns, but I'm a little confused about the last scene where the adult Mattie goes to the Wild West show to see Rooster. Cole Younger introduces himself and Frank James, and tells her that Rooster passed away a few days before. How did he know she was there to see Rooster?

Also, as she's leaving she says, "Keep your seat, trash" (or something like that) to Frank James. Was that just because he didn't stand up when he met her? Or was there some connection between the two earlier that I missed?