The same HB has sat next to 4 times, dude she WANTS to be opened, it's proximity, she's choosing to sit next to you.
Ok, 2 ways to go, depends how confortable you are with opening.
So she sit's next to you again "Wow, you must really love sitting here, next to me, Hi, I'm..."
or just say "Hi

"
I once opened a girl (Admittingly a 6.5, ok 7 if I'm being genorous) on a train, she sat across from me and started reading a magazine, I noticed it was a womens magazine and on the cover it said something like "My husband destroyed my face with an Axe" (No joke

) and I said to her
"Holy shit, who hit's people with Axes? Damn, domestic violence has changed!"
She actually looked up and laughed, we got to talking and I lead her into the "Incredible Connection" routine, started playing footsie under the table with her, number closed and a kiss (which I got due to Mystery's kiss gambit, I love that routine so much haha) as she got off the train a few stops before mine.
So it can be done. Good Luck
