These are the relationships Nicole has with the other characters in the series.
Nicole loves her son very much, and has been willing to go to great lengths to protect him from any danger that can happen. She is aware that he's not the most popular at school, so she often gives him advice or physically tries to help him, whether it be going to school with him or confronting his bully. Gumball's idiocy creates problems for her but she's willing to forgive him in the end. Even when they differ in paths, and Gumball wants to make Nicole realize her mistakes, Nicole (while tricky) still accepts Gumball's tips when he is right.
Oddly enough she doesn't interact with Darwin that much. In the show, she rarely speaks to him one-on-one. However, she does love him very much and treats him like her own son. She has shown her care for him in "The Genius," when she got angry and sad about the government taking Darwin away. Also in "The Gi," she was concerned for her sons as they were both being ridiculed by their classmates. In "The World," Darwin and Nicole are shopping in a supermarket together, implying that they do occasionally spend time together as mother and son. Also in "The Origins: Part Two," she, like Gumball, was overjoyed to know Darwin was alive and well upon his return to Elmore, she even showed her concern when she noticed Darwin's bruised feet. The relationship between Nicole and Darwin was heavily emphasized on in "The Roots," where Nicole expressed more love for Darwin than she had done in any other episode. Such as doing everything she could to make Darwin feel more comfortable in his environment (believing Darwin was unhappy), expressing great sadness when thinking that Darwin needed to be released into the wild and kissing him on his forehead while hugging him.
Nicole treats Anais on a higher standard then she treats Gumball and Darwin. Well aware that she's smarter than her brothers, Nicole tries her hardest to make sure Anais's intelligence stays intact. Often she advises not to engage with her brothers in dangerous things, and scolded Anais at the end of "The Goons" even worse than her brothers. But she loves her daughter, and was willing to change the entire family in order to make sure she is okay.
Nicole's love for Richard is rather odd, but it's still there. She's aware that Richard is socially awkward and still has memories of him being an idiot. But that does not stop her from protecting him with all her might, and taking care of him as well. On the another hand, Nicole sometimes uses Richard to control her sons, as part of making him "the bad cop" as seen in "The Password." In "The Love" she is unable to explain why she loves Richard, but the two eventually just hug each other.
Their relationship is given further exploration in "The Choices". We see how Nicole and Richard met in their adolescence. Before this, we see that Nicole had strict and controlling parents, with her mother planning out her whole life for her and demanding nothing but success from her. Until Nicole met Richard, she felt like she had to win and succeed in order for people to like her. But after she gets Richard unstuck from a log (after getting lost on her way to her karate tournament) the two begin to have a conversation, with Richard telling her people already like her for who she is, including himself, and she should just live her life. The two fall in love and begin dating through their teen years and early adulthood. Along the way, Nicole's parents do not approve of their relationship, and in her late teen years Nicole storms out after having a fight with them (much to the dismay of her mother) and at the same time Richard's mother kicks him out. The two eventually move into a small apartment and Nicole eventually becomes pregnant with Gumball, forcing them to get married. After another series of flashbacks showing Nicole and Richard raising their family, Nicole says she wouldn't change a thing about her family, including Richard.
Nicole, and Granny Jojo seem to have something against each other, like most stereotypical in-laws. In "The Kiss," she (along with Richard) drives away from the house before Granny Jojo arrives. In "The Authority," when Granny Jojo meets the family, she shows her anger. In "The Man" however, though initially showing contempt towards her mother-in-law, she eventually supports Granny Jojo and Louie dating, saying that Granny Jojo has never been so happy and kind to her.The Man", a flashback shows a young Richard, on a ladder, serenading a young Nicole outside her bedroom window. Her father is then heard yelling to Nicole, asking where she is. Nicole tells Richard to leave because her dad is coming, and she closes her bedroom window as Richard falls down the ladder, showing that Nicole's father did not approve of her relationship with Richard.
In "The Choices," Nicole's parents make their debut. It is shown that Nicole's parents, especially her mother, were determined that she would be successful and had ridiculously high expectations of her. Mrs. Senicourt is introduced in the episode by chastising Nicole about her straight-As report card, claiming that Nicole got an F in "Gender." Nicole states it's an F for female, to which her mother replies "Being a girl is not an excuse," while she clenches her fist with the report card in it.
Her father, whom despite not interacting with her as much as mother does, he is shown to be somewhat apathetic towards her, readily expressing anger in front of her when he causes the car to break down by punching the steering wheel so hard the engine flys out, and telling her to run to her karate tournament.
When Nicole is about to start running, her mother calls out "And remember!..", to which Nicole thinks she's going to say she loves her, and she tells her mother she loves her, too. However her mother says "No, I was gonna say second place is first place for losers but yeah, that too." Nicole groans and begins running to her tournament.
Nicole's mother tried to plan out her whole life, wanting (and apparently counting the minutes till) Nicole to graduate high school, graduate law school, and marry a doctor. They did not approve of Nicole's relationship with Richard. In her late teens, Nicole moved out after having a fight with her parents. After she storms out, her mother, who was glaring before, begins crying, whereas her father had no reaction besides him glaring. They did not show up at Nicole and Richard's wedding, and it seems like Nicole is still seemingly estranged from her parents.
However, Nicole has acquired a few traits from her parents, mainly her father's anger and temper and strength. She also seems to have acquired her mother's perfectionism, as seen in episodes such as "The Fridge".
Yuki and Nicole were best friends in their childhoods and were both martial arts prodigies. However, when Nicole's fiery spirit allowed her to defeat Yuki in a tournament, Yuki was dishonoured and left the US to practice more martial arts to get back at Nicole one day. When that day came, Yuki repeatedly challenged and taunted Nicole until she finally broke and accepted her challenge. However, when forced to cooperate to save their children, Yuki apologized to Nicole for letting her jealousy consume her. Nicole accepted her apology and the two embraced and became friends again.
Nicole seems to approve of Gumball and Penny's relationship. This was first seen in "The Gi" when Penny was sticking up to Gumball after everyone laughed at him. It was seen again in "The Meddler" when she attempted to be supportive by telling Penny that Gumball loved her. In "The Shell," Nicole was proud when Gumball finally confessed his feelings.
Nicole hates Miss Simian due to Simian calling her a loser throughout her life; and later tricking her children into writing a suggestion for Simian to win a "Teacher of the Year Award".