Poor Lena Luthor, honestly. The second she finds someone who believes in her and validates her own intelligence, it causes a global catastrophe. At least we know for certain now that she only wanted to do good for the planet and prove herself. Unfortunately, Daxam invaded Earth on Supergirl and Lena was an unwitting participant in the alien plan to declare "New Daxam" in National City.
This was all Rhea's doing, let's be very clear and honest. She manipulated Lena Luthor into creating a portal that not only somehow caused telekinetic chaos amongst a group of peaceful aliens — but also allowed dozens if not hundreds of Daxamite ships to travel to Earth and assemble at their Queen's command. Oops! I don't think that technology is going to be used to eliminate fossil fuel emission, bad airplane food, and train delays yet, Lena.
Perhaps getting Mon-El back on her side wasn't her only goal after all. Her people do need a place to live. They are refugees just like every other alien on Earth. It just so happens that they are lead by an evil Queen who still seeks to rule them and everyone else. That's definitely an issue. Rhea additionally lied to her son about how his father died, and then transported both him and Lena onto her ship with her. That's suspicious. What does she need the two of them for?
It's not surprising that a season about human/alien relations and extraterrestrial civil rights is going to end in a full on alien invasion. This will truly test all of the major characters, both with regards to their moral centers and as defenders of their home. These final Supergirl episodes are not to be missed, that's for sure.