As Penny and Violet are from different series, they have never met in canon. Even though a few Disney crossover games could have the two crossing paths or get added to the same team, by the player's choice.
Because of the illegality of superheroes, Violet wishes that she was normal and didn't have powers until she had to use them in order to save her family and the city. Penny on the other hand wanted an normal life for her and Bolt, as she was tired of her acting Currier keeping them apart off set. The Bolt TV show had Penny going on many adventures, while Violet went on real one's. Just as Dash saved his big sister from fire, Bolt was the one that had gotten both him and Penny help from the rescue team outside. Both of their main colors are red. As it is the main color of Violet's super-suit, and Penny wears a red top in the Bolt TV show. While their other clothes are of brighter colors.
During tough times in their lives, Violet and Penny turn to their mothers for support. In both the Bolt TV and video game, along with the Incredibles lego game, both Penny and Violet are shown to have computer skills and know their way around technology. The video games of their films, also have both Violet and Penny sneaking past masked henchman while trying to not get caught by them, while the other characters in the games fight both the henchman and bosses.
Violenny is one of the main femslash ships of The Modern/Futuristic Four crossover fandom, where the two are two of the four main members, along with Hiro from Big Hero 6 and Wilbur from Meet the Robinsons. It is often shipped alongside Hirbur. It was original the only femslash ship until a few other characters, from both Disney and DreamWorks, were added to the crossover fandom. One of the AU's where the two are paired together is a Descendants AU with Violet as Mal and Penny as Evie, while Wilbur and Hiro are Jay and Carlos. In a few Superhero AUs, fans give Penny her own superpowers, or have her as a Black Widow-like spy.
Even though the ship has a small fanbase to Hirbur and the other het Modern/Futuristic Four ships, is still has support from fans who ship them.