Pacifien - I find your idea intriguing, but don't entirely agree. I don't think it's so much a matter of ME2 revealing the "real" Liara so much as the events between ME1 and ME2 through to LotSB had Liara finding out things about herself even she didn't know.
I believe that the ME1 Liara was really very genuine, but she found, lurking beneath the great levels of determination she already possessed, a certain degree of ruthlessness that circumstances brought to the fore. One of the things in ME1 that always really struck me about Liara was the moment before dropping the Mako on Ilos (no, people ... *after* that part. Yeesh. Gutter minds). When Pressley (or Pressly, or however that's spelled) can only find a landing zone with 20 meters of clearance and Joker says he can make the drop ... the Virmire Survivor protests that this is suicide, and Liara says that you have to try. Liara is not someone who flinches from what has to be done.
I know I was very vocal about my complaints on this board about how Liara was handled in vanilla ME2, and then I kind of drifted off, because after venting, I just wanted to not think about ME2 until LotSB got released. And now that I've played it four or five times, and completely love it, I am taking this opportunity to apologize in public. BioWare, I'm sorry I was cursing your name for the 6 months between the release of ME2 and LotSB. You did a damn fine job on this DLC, and it resolved all my complaints about how Liara was handled in ME2.
At the time, I thought her behavior was explainable, if you squinted and turned your head to the side to fill in the blanks and were willing to make up your own explanation - but my main complaint was that it was jarring and wasn't set up very well. It was far too drastic a change without anything to back up or explain how/why this happened. LotSB fixed all of that for me. And, well, getting a paragon-interrupt where Shepard gets to snark about hacking terminals sure didn't hurt.
All in all, I find her character arc both believable and interesting - and I think there's no way she isn't going to play a big role in ME3 as a squaddie or information source that would let Shepard blow off both the Council and Cerberus.
I don't even find her fixation on the Shadow Broker off-putting anymore, because at this point, it just kind of feels like it comes from survivor's guilt regarding leaving Feron behind to rescue a corpse that may or may not result in Shepard's resurrection, and a dedication to cleaning up her messes. And, really, if there had been the possibility that the Virmire Non-Survivor hadn't actually died but was - maybe - being held prisoner somewhere, I think my very paragon Shepard would have pulled out all the stops to rescue or avenge VN-S. I respect Liara's commitment to her teammates, now that the motivations are better explained.