Penny tells Ruby Rose that she was created by her father in "Painting the Town..." with help from James Ironwood. However, nothing else is known about him. She appears to love her father very much, calling him "very sweet".
Penny first takes a liking to Ruby in "The Stray", when Ruby calls her "friend". Excited and eager to have a friend, she asks Ruby for confirmation on their relationship being a friendship, to which Ruby replies "Yeah, sure. Why not?" Although quick to call her a friend, Ruby does seem put off by Penny's excitement over it and even asks Weiss Schnee if that was what it was like when they met.
Penny admits to Ruby that she does not have a lot of friends, and thus greatly treasures their friendship. She is also extremely protective of Ruby, going as far as to jump into a fight in her defense when she was injured in "Black and White", and as seen during "A Minor Hiccup", where she pushes Ruby out the way of an incoming truck before stopping it in its tracks, visibly shocking Ruby.
Penny considers Ruby to be a valuable friend, placing a high amount of trust in her and going as far to tell her that she is not a real girl. In "Painting the Town..." after revealing such news to Ruby, Penny was surprised by how the news was taken by Ruby, who stated that she did not care, for she was still real and carried both a heart and soul. Penny was overjoyed at the fact that her friend still accepted her as a person, and wrapped her in a tight hug, saying she was the best friend anyone could have. Also, in Never Miss a Beat, she tackled Ruby in a hug. Likewise, Ruby was devastated over Penny's destruction in "PvP", dropping to her knees and sobbing.
It appears that Penny is exaggerated for the reason that she told Ruby: she does not have a lot of friends. This is possibly due to her being isolated, given that she has had no time to socialize.
In RWBY: The Official Manga, after Ruby accidentally bumps into her, Penny extend by her hand and asks Ruby if she is alright. She then proceed to get closer to Ruby and asks her to be her friend. However, Ruby does not give a proper answer to Penny and cannot say no. This make Penny believes that Ruby became her first friend and she appears very excited to do things with her. In Chapter 8, Penny decides to help Ruby and destroyed most of the White Fang's airships. She later tells her the reason why she fights because she wants to protect her friend.
Weiss runs right into Penny while chasing down Sun Wukong. She expresses skepticism when Penny says she is going to be in the combat tournament.
Both she and Yang Xiao Long run off after Penny arrives to talk to them while they are looking for Blake Belladonna, apparently not wanting anything to do with her. It appears she has an admiration for Weiss' hair on the second day they meet.
However, later in the series it appears that Weiss has made a small connection with Penny, feeling sad about her death.
Due to Penny's odd and robotic behavior, Yang finds her bizarre to the point of neglecting the pleasantry of a simple introduction until Blake Belladonna reminds her. Both she and Weiss quickly run off when Penny shows up to talk to them while they are looking for Blake, indicating a lack of interest in associating with her.
In "End of the Beginning", Yang was remorseful towards Penny after her identity was revealed as a robot when she was destroyed by Pyrrha.
Ciel is part of Penny's team in the Vytal Festival Tournament. After their team progressed past the team stage of the tournament, she and Penny were selected to represent them in the doubles round. Penny states that Ciel was told to be Penny's friend and as such is more of a bodyguard to her. Ciel keeps track of all the places Penny is and for how long she is there. Because she does not see Ciel as a true friend like Ruby, Penny has not told Ciel that she is a synthetic being.
When Penny and Pyrrha are about to compete, Penny expresses pleasure in finally meeting her. Those who are aware of both Pyrrha's Semblance and Penny's true nature know that the two of them competing against each other has the potential for disaster. Subjected to a hallucination by Emerald Sustrai, Pyrrha uses her polarity with extra strength to deflect what she sees as an abundance of swords about to strike her. Penny is destroyed as a result. Pyrrha is left horrified and devastated after seeing what she has done.
Cinder discovers through her computer virus the truth about Penny's nature. She shares this knowledge with Emerald and Mercury, and presumably comes up with the plan for her destruction.
Mercury prevents Ruby from attempting to stop the match between Pyrrha and Penny, taunting her about it.
Penny first sees Roman Torchwick when she and Ruby arrive on the docks in "Black and White." At first confused by his casual greeting into wondering whether he is Ruby's friend, she immediately becomes focused after he shoots Ruby. She jumps into the fight, quickly neutralizing Roman's men, which makes him decide to escape. Her fighting style prompts Roman into commenting that "these kids just keep getting weirder."
At the end of "Black and White", Penny is collected by the driver of a black car. The driver reproves Penny for taking risks by going out alone. This individual is unidentified but Penny refers to him as "Sir" in a subdued tone, implying that he has a strong position of authority over her.
In RWBY: The Official Manga, when the driver asks her how was her pleasant walk and Penny replies she was fine with a sadden smile.
Penny is seen standing with James and a group of other Atlesian military personnel in the Volume 2 Opening. He is revealed to have assisted and sponsored her father in her creation, with the hopes that she will one day be able to save the world. Penny is also seen following Ironwood around in "It's Brawl in the Family."
Although she runs away from them at first, she does not appear to have a poor relationship with the Atlas soldiers. When Ruby expresses concern about her going with them, she says that "They're not bad people". She is shown respecting them and following their orders. She is also shown to be doing "the robot" with one of the soldiers in "Dance Dance Infiltration."