After Siobhan learns that Kara Danvers is Supergirl she will then explain to her or anyone else close to her that is still around about her family's curse and why she was trying to kill Kara other than losing her job which explains why she was acting strange after the DEO scientists confirmed she wasn't an alien and to why she came back into Catco and attempted to kill Kara and tells Winn that the curse was triggered because he hurt her feelings when he kept her from making Kara lose her job and after explaining to her that Kara is Supergirl and everything that has happened last year since the explosion at Lord Industries tower.
After Winn gets kidnapped by Macdougal, Siobhan puts on her costume and makeup as Silver Banshee and she and Supergirl will go after the evil Banshee in Scotland while Superman, Superboy Martian Manhunter, and Miss Martian deal with Doomsday in Metropolis while the DEO is dispatched to arrest the doc and everyone in project Cadmus as Olsen and Lucy stay in National City to make sure it is safe incase they have been given their powers by Cadmus and have just begun using their abilities and have donned their superhero identities.
Now for how the Silver Banshee MacDougal later in the season 2 finale is to be taken down. As soon as Supergirl and Siobhan reach Agatha's castle in Scotland and then find her in the room she was keeping Winn and her family in, MacDougal will have begun conducting the ritual as she kills Sinead in the center of the room with a dagger infront of everyone leaving them shocked and horrified by her death but just as Agatha drags Winn into the circle and is about to kill him next, Siobhan intervines by blowing her away from the circle and frees him and the rest of her family while Supergirl keeps MacDougal busy as she brings her over to Dublin and as she subdues her with a device to keep her from unleashing her Sonic Screams, Kara then gets Agatha to confess everything she did over the last 10 years infront of a nearby crowd recording the conversation with smart phones which were streaming the videos live so that the world involving National City will know of her crimes on what she did to ruin her life and Siobhan's and for everything she had Project Cadmus do since she found out about her but after getting her explain everything she did and her reasons for doing so, MacDougal then breaks free and removes the device from her neck and after overpowering Supergirl, she then teleports back with her to the castle and just as they got back with everyone else gone, Agatha then grabs a kryptonite sword she had Cadmus take from the DEO, she severely wounds the girl of steel with a few slashes and vows that after she kills her she will go after Superman and the rest of their friends and families and make sure they die as well but just as she is about to kill her with it, she is to be stopped and implaled through the chest by the same dagger she killed Sinead with from behind by Siobhan who will then understand that Kara was never her enemy and tells Agatha that just by letting all of her rage over the setbacks her uncle and brother caused her 15 years ago consume her with madness that she is nothing but a monster and when MacDougal tries to retaliate, SIobhan then disarms the kryponite sword from her grasp and kills Agatha with it either by slicing out her throat to make her succomb to her wounds or by decapitating the evil banshee with it to end her madness once and for all and by doing so Siobhan was finally free from the curse before it almost took her over and then helps Kara up and brings her outside for the sun's energy to heal her while he apoligizes to her for vexing her at work and for trying to kill her without realizing until now that Agatha had been stalking them for years and explains that she killed her not just to lift the curse from herself but primarilly because after all the trouble the sinister Silver Banshee caused for them, all the lives she took and all the damage she has done that Supergirl was too good a person to go down for scum like her and Kara apoligizes to Siobhan for mistaking her as a bad seed as the two then give eathother their condolences for the people in their families that have died in vain. Then the same banshee that had cursed the Smythe family will appear and apoligizes to Siobhan for all the trouble MacDougal caused her that she was willing to make it up to her that if she ever comes to Ireland during the week her family attends Sinead's funeral she will grant Siobhan power with the spell that MacDougal was never able to complete and with it not only will Siobhan be able to fly, move super fast, become superstrong and posess the ability to unleash sonic screams for combat and teleportation but will also allow her to change into her banshee form and revert back to her human form whenever she wants. as well as being able to speak in many different languages like she does in the comics and it won't take her over like the curse does. As Siobhan gladly accepts the offer that she was willing to do more good for others than just herself, Supergirl will then leave them both to help her family and Winn get to Ireland for her aunt's funeral as she flies over to Metropolis to help Superman and the other heroes that are with him defeat Doomsday so they can finally put a stop to the destruction and threats that MacDougal had Project Cadmus bring upon them once and for all. And in the end of the season 2 finale, Kara along with her sister Alex and her mother Eliza and the rest of their friends attend Jeramia Danvers' funeral over in National City, Siobhan had started training with her new powers given to her by the spell that the Banshee (whose real name is yet to be revealed) completed for her and is currently teaching her and other girls with them on how to handle and use their abilities wisely as they went with Winn and the rest of the Smythe family to attend her aunt's funeral while they still in Ireland. And in the final scene, Supergirl will narrate a dramatic point of view that "Even though things don't work out the way we hope or want, we cannot let that setback or anymore that are ahead control our future. Sure there will be more consequences and bad days that lie ahead for one another but no matter the loss, no matter the difficulty, and no matter what happens, we always need to keep moving pass them and set our sights and dreams onto newer and better things in life. I am Kara Danvers, also known as Supergirl."
And while Kara is set to take on a new major threat in season 3, Siobhan will be needed along with other heroes throughout the Arrowverse to appear in the final 3 episodes for Flash season 4 to help them and Barry defeat Zoom and his army of metahumans in another Metahuman war. Now in order to find out if CW will make sure this happens, we just need to keep watching episodes and previews to the new season of Supergirl starting tonight at 8 pm.