Elena Validus

Elena Validus is the daughter of ex-Plumber who appeared and had a large role in the live-action film, Ben 10: Alien Swarm. It is known she'll be in the next ultimate alien episode also her dad Victor Validus will appear.

Ben 10: Alien Swarm
According to the movie, she hung out with Ben and Gwen. During this time she and Ben became close, Ben helped her join the school soccer team, speaking up for her when the other players wouldn't let her join. She eventually became the team's MVP. Gwen told Kevin that Elena was Ben's first major crush, but she was force to leave Bellwood after her father was caught stealing alien tech from the Plumbers (Max never told Ben or Gwen why Elena and her father moved away). She eventually discovers her father had been taken over by the Hive Queen and seeks help from Ben and the Plumbers.

She sets up an illegal alien tech deal, in the hope that the Plumbers would catch her so she could warn them about the alien chips(inert members of the Hive). An undercover Kevin, acts as the buyer along with Gwen and Ben. Elena reveals herself to Ben and Gwen, who are stunned by her sudden reappearence. They are then attacked by Victor Validus/Hive Queen who actives the inert alien chip. Ben 10: Ben defeats the alien chips as Big Chill, and Validus escapes. Afterwards Ben, Gwen, and Kevin talk about what has just happened. Though Ben trusts Elena, Gwen and Kevin don't (believeing she set them up). Elena secretly follows them to Max's Plumber HQ.

At Max's Headquarters, she detected sneaking inside of Max's office and caught. She tries to explain herself, but Max tells Ben and the others they can't trust her. Her plea for help rejected, she is lead out by Kevin.

Riding her motorbike, she is stopped by Ben(riding Max's motorcycle) who decides to help her find her father, against Max's orders. They head to her fathers secret lab to search for clues, but are attacked by humans enslaved by the Hive. They barely escape, as Elena crashes her bike, and is forced to ditch it. She climbs onto Max's bike with Ben and the two of them flee. They are on the way to the warehouse of a shipping company(called "Ship-It") her father was using, when they encounter Kevin and Gwen being chased by swarm of alien chip. Ben saves Gwen and Kevin(destorying Kevin's car in the process). Elena shows them some of the alien chips they found at her fathers' lab, and they all head back to HQ to study them. They are confronted by Max who angered by Elena presence. Ben, Gwen, and Kevin show him the active chips, and realizing Validus may have been right along allows Elena to help them.

Ben later discovers one of the chips is missing and is attacked by an enslaved Max. Max is subdued by Kevin but later escapes. Elena and the others locate where the alien chips are being produced, Ship-It's main destribution hub.

Elena, Ben, Gwen, and Kevin sneek into the main warehouse, where they discover Validus hooked up to a machine. They see Validus producing the chips from his body, revealing to everyone that he is the Hive Queen. Gwen and Kevin confront, Elena who reveals she knew it all along, but didn't tell them because she was afraid she wouldn't be believed (just like how the Plumbers didn't believe her father).

Gwen and Kevin believe sacrificing Victor is the only way to stop the Hive and save the world. Elena pleads with Ben to save her father. Ben tells them he will use the Omnitrix to transform into a member of the Hive(having realized that the Omnitrix had been scanning the Hive chips earlier). He uses the Omnitrix to transform into the alien hero, Nanomech. As Nanomech, he travels into Validus' body and defeats the Queen, freeing him from its control. Elena hugs Ben and thanks him for sparing her father's life. As they are leaving to return home she says she plans on joining the Plumbers, and gets into an silly argument with Gwen.

Ben 10: Ultimate Alien
She appeared in Revenge of the Swarm. After Ben was repeatedly attacked by nanochips in the form of Victor he investigates to the Validus Laboratories accompanied by Kevin and Gwen. A smirkish with the janitor led them to come to terms with Victor's death however they are skeptical of the claim. They traveled to Plumber's Academy in hopes to find Elena who knew most about the chips. Despite being one of the best students she dropped out of the academy in order to pursue her father's research. The trio went to her laboratory and Ben was greeted warmly by Elena. She explains that the nanochip Ben saved wasn't hers and that she would not want to go over these matters as her father's research matters more. Kevin and Gwen were attacked by Viktor's nanochips form and Ben comes to rescue them. The nanochips flee somewhat giving the expression of not wanting to fight Ben. They went to the cemetery where Gwen confirms that Viktor is truly dead. Elena surprises them with her choice wanting to help them over continuing her experiments. They went over to Mr. Smoothy where Ben mentions Julie which irked her. The nanochips then kidnapped Julie. Ben confronts Elena with the nanochip he found and berates her. It is revealed that she lied and that her true intentions were to have Ben all to herself even if it meant harming everyone that stood in her way. She transformed into the Queen's form and prevents Ben from getting to a storage where she locked up Julie. She admitted that the Queen Ben had killed earlier in Alien Swarm was just a decoy and that the nanochips had reside in her since a long time ago making her their queen. Ben retaliates and frees Julie. Elena generates nanochip clones of Victor to attack Gwen and Kevin after they found out that Elena is the Queen on their own prior to their arrival. She has Ben on death grip within the nanochip's grasp. Julie reasons with her if she did ever truly cared for Ben she would've stop this. Elena still having feelings for Ben agrees with her. She sacrifices herself despite Julie's calls and was destroyed coming into contact with the nanochip force field she showed earlier. Julie tries to console Ben saying that the nanochips took over her while he said she was still his friend. At the end, a couple of the nanochips are still active. Elena might have survived

Powers and Abilities
Unlike other Plumber's Kids, Elena is completely human. Despite not having any special powers she is a capable fighter and an exceptional martial artist(skilled in both armed and unarmed combat). According to Ben she is also great athlete, becoming their school Soccer team's "Most Valuable Player". It could be assumed she was trained by her father before he became host to the Queen.

Trivia

 * She appears to be slightly xenophobic, possibly due to her jealousy of humans of alien descent and their special powers (like Gwen and Kevin). When introducing herself to Kevin she explained she was human and wasn't a freak like them(referring to Kevin and Gwen).
 * She appears to have something of a friendly rivalry with Gwen, similar to the current rivalry between Ben and Kevin.
 * A plot hole in Alien Swarm was that, during the Humungousaur scene, she knew Humungousaur's name, despite Ben not saying it when he transformed. Though it is possible that she heard it off the news or that Ben may have told her about all of them off screen.
 * Elena was also seen in Ben 10 continuity of the comics.