Need some help with a TDR - Pandoras Box

Looking for some help from someone who is familiar with Vin's pandora's box.

There is this girl in my grade that ive been chasing for a while now. We are spending quite some time together, where quite good friends. Im trying to stay out of the friendzone. Since she is a tdr she enjoys guys company and likes attention so I dont think she has friendzoned me to the level of no return. Getting alone time with her isnt a problem, the problem is moving on from there. I dont think she has that much interest in me at the moment, however she can talk to me about personal things that a tdr usually wouldnt talk about with anyone (still pretty sure im not friendzoned though).

I know she is dating another guy but its not going to well between them, hes an ass most of the time (prob why she is hooked on to him), and they havent had sex yet.

This is a difficult situation for me, its not that i cant Pick Up Girls, its just that i see her as "girlfriend" material so its not like picking up any girl for a One Night Stand...

Help would be MUCH appreciated...

Ps i know i have to try and sleep with her as quickly as possible, but how do i go about with this?