Leni Loud/Relationships

Her siblings generally
Her younger siblings see her as a very sweet and kind-hearted older sister, contrasting Lori, but her ignorance and clumsiness can sometimes cause harm irritation for them, as much as they know she doesn't mean for it. When her siblings are in need of assistance, she will always come to their aid without letting her ignorance get in the way. All-in-all, they love her very much and take very good care of her.

Lincoln
Leni and Lincoln get along very well. Most of their interactions are generally positive, despite Lincoln getting annoyed with her from time to time.

It's noteworthy to point out that Leni has been shown to be very accepting of Lincoln's odd white hair, shown both in "Chore and Peace" when she said it makes him look like their grandfather, Pop Pop, and in "Ties That Bind", where she defends it when their parents seemingly decided to "get rid of" him. Along with Luna, she has the healthiest relationship with Lincoln out of all the Loud sisters.

In "Driving Miss Hazy", he helped her to pass her driving test by using her semi-language. He also convinced her to not give up trying.

In "Along Came a Sister", Lincoln brought his class's pet tarantula home for the weekend and Leni attempted to kill it, due to her fear of spiders. However, after she learned Lincoln will get into trouble if he let his class' pet die, she protected it to save her brother's status quo, showing how much she loves her brother.

In "Linc or Swim", she was always the first one to invite him to spend time with his other sisters. First, to "chill" with them next to the open fridge, second, in to the "Paradise for One" pool he had set up (this shows how nice Leni really is compared to the others, unconditionally offering him to get in to the pool with her and Lori) and third into a newly purchased pool even though he kicked them out of his.

In "House Music", the siblings decided to form a band, and while all the sisters left Lincoln ends up getting hogtied to the floor, thanks to Lana, Leni was the only one who returned for Lincoln and apologized to him, and she carried him like a handbag, much to his annoyance.

In "One Flu Over the Loud House", Lincoln sacrifices himself to protect Leni from becoming infected with the zombie flu. When she asked why he did it, he tells her that it's because she has a good heart.

Lori
Although Leni and Lori differ from one another in both kindness and intelligence, they are actually very close. They are both enthusiastic about fashion, taking selfies, and talking about boys. Despite this, Lori will often try to control Leni and boss her around. At times, it seems as though Lori takes advantage of Leni's ignorance and naivety and makes her complete tasks that she should have done herself.

In "Driving Miss Hazy" Lori didn't want Leni to pass her driving test because then her siblings would ask Leni to drive them places instead of her; therefore she would no longer be able to get them to do favors for her. She sabotaged Leni's driving test but later she felt extremely guilty for her thoughtless actions and wanted to fix her mistake by helping her prepare for her next test.

In "It's a Loud, Loud, Loud, Loud, House" they both teamed up to search for hidden money in their house. They were seen dancing together at the end once the money was found.

Luan
Luan gets easily annoyed by Leni's stupidity as much as Leni gets annoyed by Luan's bad jokes. Luan often scares Leni with her plastic spider.

Lisa
Lisa often uses Leni as a test subject to prove her experiments and inventions. The reason of this is because of Leni's poor intelligence. This is evidenced in various episodes like in "Project Loud House" when Lisa changed Leni's blemish cream for an experimental skin pigmentation ointment, turning her skin blue.

In "Butterfly Effect", Leni becomes smarter than Lisa after being hit in the head with a coat rack. This caused Lisa to give up on science, and gets a job at a gas station.

Given their completely different IQ levels, Leni's stupidity tends to get on Lisa's nerves at times.

Lily
She and Leni have a good friendship, and second to Luna is the one who holds Lily the most. In "Changing the Baby" Leni tries to implement her interests on Lily because she had nobody that share her likes.

Clyde
Clyde and Leni's friendship seems to be pretty good. In the segment "Overnight Success", she asks for his help on a new facial cream she needs to test on before trying it. She also seems to enjoy his company at the sleepover.

In "Along Came a Sister", Clyde recalls one time on Halloween when Leni mistook his spider costume for a real spider and sprayed him with bug spray. Of course, this was just her arachnophobia getting the better of her.