And one question : Why Talia whould care about The Queens when she loves Bruce Wayne ?

IGN: Before we go, there's a question a lot of fans are curious about. I don't think the answer is yes, but I have to ask it... Now that they've mentioned Ra's al Ghul and his child, people are speculating that Isabel is also Talia al Ghul. Anything you can say about that theory?

Glau: I have heard that theory, but I don't know... I really don't know any of the secrets about what's going to happen after this last episode that I was in. I wish I could help unveil some more secrets, but they keep them from me too!

There are several reasons why I think this Isabel Rochev is Talia al Ghul.

1. Because nothing in ARROW is at it seems.
2. There is an episode late in Season 1 in which Fryers phones into an office somewhere in the world. There is a woman sitting in a conference room with her back to us, she doesn’t speak. We only know it is a woman when she crosses/uncrosses her legs. Then a few episodes later Isabel turns up, coincidence? I think not.
3. Ep2.01 Moira knows of Isabel Rochev - she says that she is not to be trusted.
4. A feeling, that is all i can say. Others too think that this is the case.
5. She seems to know more about Oliver Queen than someone might normally know. There is something very mysterious about Isabel.
6. It’s even more suspicious that her sister is now going to be turning up in Starling City in later episodes of season 2,
7. Isabel Rochev is on the List. So why would Robert put an ex-lover on the list?
8. The creators stated recently that they never mention a name and then not to have them appear. So we can expect Ra’s al Ghul to appear as well at some point.
9. When creating ARROW the creators took inspiration from several sources, one of which is The Dark Knight series (Batman Begins). (NB: Batman is a DC Comic character) Interestingly in the third instalment of the movie, The Dark Knight Rises - Batman is taken in by Miranda Tate (played by Marion Cotillard) who is a member of the Wayne Enterprises executive board who encourages a still-grieving Bruce Wayne to rejoin with society and continue his father’s philanthropic works. Later on in the movie, While the police and Bane’s forces clash, Batman defeats Bane, but Tate intervenes and stabs Batman, revealing herself to be Talia al Ghul, Ra’s al Ghul’s daughter. (Does some of this plot line sound familiar, hmmm). Another prediction, can we expect Isabel/Talia to stab Oliver Queen in the future, as the creators nod to this movie?
10. Summer Glau looks very much like Talia al Ghul from the comics.

Who is Isabel Rochev really?

While the mere mention of Ra’s ah Ghul was enough to send season one Big Bad Malcom Meryln running, the Demon’s Head might have already had a more tangible presence on Arrow via Summer Glau’s corporate shark character Isabel Rochev, who many have speculated is really Talia ah Ghul, in a Dark Knight Rises-like twist. However, the reveal of a corporate suited (rather than body armored) Slade Wilson in the modern timeline might throw water on that theory. Ra’s isn’t the only villain with a child; it’s possible that Isabel Rochev is instead really Slade’s daughter Rose Wilson. An Isabel is a type of Rose after all.

Since Slade’s plan was to take everything away from Oliver and that would include his family’s company, in comes Rochev who nearly accomplished this. Despite failing to take over Queen Industries, she has stuck close to him Oliver gathering information and as seen in during Team Arrow’s adventure in Russia, driving a wedge between Oliver and Felicity.

Naturally all of this is pure speculation, but its these little details that keep up watching these shows after all, and looking for the next little clue.