Boyfriend shit-test or not, what's the best approach

I've known a girl from a class for nearly a year. We'd never really hung out, but had plenty of smiles and Hi's since the class, we just ran in different circles and never really had an opportunity. About a month ago I ran into her a party, chatted with her quite a bit until the uber-AMOG came up and started making an ass out of himself and her. I assumed he was her boyfriend, but I couldn't stand the creep coming off him and had fun elsewhere in the party.

Two weeks ago I run into her again at a bar during my second night really trying to game a particular girl. Mostly as social proof, I chatted with her and the uber-beta guy she was with. I noticed halfway through that I completely dominated the other guy out of the conversation. Her body posture, kino, and the eye contact all shifted to me. At some point I even unconsciously blocked him out of the conversation moving between the two of them.

At Halloween she showed up at the party I was at, we chatted a bit, same beta-man hanging on the edges. I skipped to a different party for a while, but came back after an hour or so. By this time, I'd passed gaming ability by a beer or three and was just having fun. We talked for a while, until her friends grabbed her to go. I grabbed her back and got a quick kiss to end the night.

A bit later I texted her my number. The next day she responded saying I was fabulous but she was seeing someone. We've texted several dozen times since Sunday. Spent 3 hours Tuesday walking around campus, grabbing coffee, and laying in the grass in the park. She met me after work today for coffee again, and we have plans for Sunday.

I know the boyfriend line is sometimes a shittest, so I never responded to that directly. Thing is it's also sometimes true, yet I'm getting a lot of IOI from her and I am interested but prone to over-reading signals. What approach would you use to return IOI, and would it be different if her "boyfriend" is the alpha or the beta MOG?