SPOILER The identity of the mole.

In episode 3x07 "The Pickett Line" it is revealed who's the mole. Many people after seeing that Hal had a parasite inside, and have it taken away, thought the story of the mole had come to an end. But that has not happened.

The writers of this series have always proven its worth, never, repeat, they never write things obvious or easy to solve. If Hal had been the mole ... Does everyone happy and keep killing aliens? No! What would have done the Mason family if they don't have to suffer a little to keep going?

Prior to the issuance of that episode, they told us that we will know who is the mole, and began the guesses. Many people bet on Marina, Jeanne, Denny or even Pope or Weaver.
Somewhat ironically, when from the beginning one of the most repeated names was that of Lourdes. But I think that, having posted in the show's official account a picture about her, talking about the mole, made many people believe that it wouldn't be her. In fact, that might be the reason why they have published this picture, to confuse us and divert our attention from Lourdes and, therefore, that I, who argued for Lourdes from the start, I ended up thinking it might be Weaver or Jeanne. But my logic is not failing me, and as I said in a previous article, Lourdes was the great suspicion, at least, if we followed the script that writers often use in the story of the show.
Any character who is still alive from one season to another, it is because it will have more prominence or be relevant to the story. And there's the case of Lourdes, and being the mole was the reason that is still alive in the series and the writers have not killed her.
 But leaving aside the theoretical reasons, let's see the behavior of Lourdes this season:
Lourdes showed a special interest, when Maggie told him he thought Karen had done something to Hal, was too obvious that she was interested in that subject, not as a doctor ... Or as a friend, it would be difficult to understand since Maggie and Lourdes does not have a great friendship ...
Being a doctor of great confidence has been the key so that no one would suspect it. She could freely say that Hal had nothing, or that Alexis was normal, there was nothing unusual, no one to stand in doubt.
Who would not trust her? So many successful results, having clear evidence that neither Hal nor Alexis were fine, it was another great track.
Do not forget the great work that Lourdes has done to be able to take away the spikes to children, who are one of the main enemies of the skitters and Espheni, and these kids are a great force against the aliens and for humans . Without them, Espheni would have more chance of winning the war.
Being the doctor has allowed play multiple cards without anyone to think that she was acting for any other reason than to help. When in reality, her motives were entirely different.

We also saw that the girl is full of bugs, which, I guess they control her mind and acting on her. Now we have to figure out how they got those bugs to Lourdes. All people say, "How they have been implanted by Karen? Does she kissed her?". What a  longest kiss to pass so many bugs ... And, as I always say, it would be too obvious if Karen had implanted the bugs to her.
I bet because the issue of Lourdes comes from before Karen was the "bad girl".
A move that took time and patience, which, do not forget, is the specialty of the Espheni.