Chili has difficulties with maintaining relationships which is shown clearly through her behaviour with others she considers 'friends', possibly due to watching her parents who she said didn't get along very well.
Chili had a twin sister known as Jellybean (Alyssa). She ran away from home when Chili was young and later ended up working as a CI agent with Antonio (Gabriella's brother). She was found dead in her apartment in season 4, something that took Chili into a downwards spiral and eventually cost her her job as she couldn't handle the grief.
Season 3 Edit
When Chili joins Firehouse 51, despite the at-the-time cold welcome, she tries to make friends but doesn't have a lot in common with the others. This is until she reveals she's in-midst of creating and designing a button on the side of beverages to cool them instantly in 5 seconds. Being a business investor, Herrmann immediately jumps in and tells her she can sell it at Molly's as soon as she's finished. He helps her a lot until Sylvie and Dawson tell him to calm and slow down since Chili's spending all of her money on it without leaving any to pay her bills. He says this to Chili who thanks him for his help, saying Herrmann reminds her of her own father who died but created the idea in the first place. They get emotional and he says he will be right with her.
Herrmann and Cindy gave Chili Molly's funds to help her idea, for which she is very thankful. They then celebrate their success when she finishes her design and test to see that it works, which it does. However, she's left deeply hurt and upset when they find that someone else has already created and launched it on TV. She cries but Herrmann tells her she will definitely come up with something else and hugs her.
She also starts dating Jimmy at the end of season 3 and they're both happy.
Season 4 Edit
At the start of Season 4, Chief Boden is under watch and investigation up to the point he is arrested and demoted from Chief and replaced by Dallas Patterson. When Casey then sees Chili and Jimmy hanging out too closely with each other around the firehouse, he tells Jimmy to slow things since it isn't appropriate while they are under watch, especially with Patterson. Jimmy tells Chili this and she is okay. However, she shows inappropriate behaviour again and when they're caught by Patterson, he gets worried but she laughs it off, which angers him and they break up.
Throughout the next few weeks, Chili behaves erratically and is constantly angry and raging at anyone who asks her anything or questions her. Sylvie assumes it's the breakup or the fact that Herrmann is in hospital but Jimmy tells her he doesn't think it's either of those. A brief moment of her crying in the hospital waiting room is shown but the reason still isn't revealed.
The next shift, the house is on lockdown from a tornado warning. Jimmy asks Chili if they can be friends to which she agrees, but the next second, she lashes out and tells him he isn't worth it and that it's unbelievable he would break up with her just because Casey told him to. During a call later that day, Chili mistakenly injects a seizing victim with morphine instead of valium, which causes the girl to stop breathing altogether instead of stopping seizing. She zones out after this and Sylvie takes over, properly injecting the patient and therefore saving her life. Chili says it's no big deal. At the hospital, she lies to the attending when she says the reason the woman has morphine in her system is because she accidentally knocked over a bottle, causing it to break. Sylvie tries to talk to her about this later but she brushes her aside and is making plans to go out. Wary and finally tired of her behaviour, Sylvie reports her actions and the syringe accident to Chief Boden.
While at Molly's, Dawson is talking to Antonio who tells her that Chili's sister Alissa was found dead in her apartment a week ago. Boden asks her about this and she says she is fine, he gives her the second strike for the syringe incident though. She then apologises to Dawson and Sylvie for acting rudely towards them and they accept. However, they see her drinking the next night and are disappointed. She starts up again and during a call, Sylvie ignores a direct call from Chili, who then tells Boden she wants Sylvie gone. Sylvie also finds out that Chili was asked to leave from the last house because of her problem. Boden gets angry hearing this and asks her to work things out or she'll be gone from 51 too. They both work things out at a later case where she apologises to Sylvie for nearly replacing her.
Things go downhill again when Chili receives a package at her day off containing all of Alyssa's belongings and she breaks down again. She then starts to make a habit of taking small breaks to drink and then come back and spray some breath spray and chew gum so thy people don't notice. However, Severide notices her constant breaks and tries to talk to her but she ignores him and Sylvie tries to look past her issues. However, Severide eventually catches her out and tells her to talk to Boden or he will. She goes to see him and tells him she needs help and is willing to take time off to go to counselling but he fires her instead. He then tells her to ask for help and she says she just did and they did nothing. She goes to her locker and the whole of 51 follow, trying to talk to her. She says they aren't her family and leaves, including leaving her photos with them behind. Herrmann gets one of the photos and frames it and takes it to her apartment. He tells her through the door that she can always come to him and leaves the picture behind.
Chili calls someone and tells them she needs help. It's revealed it was Severide, who takes her to counselling and is glad she called. She tells him she'll call them and apologise. She thanks him and she goes to rehab.