A woman asking if it’s “unreasonable” to want a lock on her bedroom door is being backed online.

Sharing her frustration with Mumsnet’s Am I Being Unreasonable? forum on January 8, user Aeroflot21 explained that her sister—and housemate—has been pilfering her clothes and taking over her room while she’s out.

However, her live-in landlord won’t allow tenants to put a lock on their doors, as it will change the terms of the rental agreement.

“I live in a house share with a couple of friends and my sister, and my sister keeps on coming into my room and taking my clothes when I’m not there,” she said.

“When I see her wearing them, she either lies and says she’s not wearing them, or she’ll insult me, or she’ll apologise and say she won’t do it again.”

Two adult sister's arguing on a sofa
A stock photo of two adult sisters arguing on a sofa. One woman is tired of her sister sneaking into her room and stealing her possessions while she’s out of the house.
AntonioGuillem/iStock/Getty Images Plus

The situation escalated recently while the pair were out celebrating a friend’s birthday. Her sister showed up wearing one of Aeroflot21’s dresses, which was the final straw.

“She denied it and said it was something she’d bought herself recently, but I knew it was mine,” she wrote.

“I tried to search for the dress in my room later, and it was missing, so I knew the dress she’d worn was actually mine.”

The sister’s boundary-stomping behavior extends beyond clothes, with her sister “using [Aeroflot21’s] room whenever it suits her.” The poster is going on vacation in a few weeks, and is expecting her sister to treat her room like a “free hotel” while she’s away.

Aeroflot21 asked fellow users if a lock on her bedroom door was too much to ask. While most agreed it was a rational request, they also believed the real issue was the poster’s sister.

When Sibling Rivalry Continues Into Adulthood

According to Chase Cassine—a behavioral health specialist at DePaul Community Health Centers in Louisiana—the dynamics of adult-sibling relationships are set in childhood, and often influenced by parental favoritism.

“Whether this feeling is real or perceived, it has been shown to be an indicator for competition and rivalry amongst siblings,” he told Newsweek.

However, expectations and labels—even if well-intentioned—can also pit siblings against one another and lead to toxic comparisons, especially if one sibling is considered the “golden child.”

Brother and sister pointing at each other
A young brother and sister pointing at each other, while the mom asks who is to blame. Sibling rivalry often begins in childhood and can be fueled by parental favoritism and expectations.
EvgeniyShkolenko/iStock/Getty Images Plus

“Parents play a vital role in cultivating a healthy sibling relationship,” Cassine said.

“[They need to] teach and model healthy ways to express their emotions and constructive ways to resolve conflicts, as these fundamental life lessons will help them in other relationships.”

But what if you’re an adult and you’re stuck with a toxic sibling? There might be time to turn things around.

“First and foremost, acknowledge your feelings, because this has been years and decades-long of built-up resentment and anger,” said Cassine.

“Use ‘I’ messages to communicate your feelings and needs without pointing the finger, [and] be mindful of your tone, timing and delivery.”

If you have a family dilemma, let us know via life@newsweek.com. We can ask experts for advice, and your story could be featured on Newsweek.

‘She’s Getting Away With it Because She’s Your Sister’

In her post, Aeroflot21 said her sister has been sneaking into her room while she’s not there. As well as taking her clothes and lying about it, her sister also treats Aeroflot21’s room like a “free hotel,” as her own room is too much of a mess to live in.

“I find it really difficult to deal with, because I see it as a big invasion of my personal space and privacy,” she wrote.

“I really try to take care of my room and my things, whereas she doesn’t. I find it really disrespectful that she just doesn’t care.”

The sisters are in their late 20s, with the poster at the “end of her tether” with her sibling’s behavior.

Some users suggested talking to the landlord to see if she can help resolve the situation.

“Tell your land lady your sister is going in your room and taking your things without permission,” advised AllAJillSandwich.

“She’s getting away with it because she’s your sister, if it were a stranger she wouldn’t.”

Mathanxiety agreed, writing: “It’s odd imo that your room can’t be locked so I would have a word with your landlady.”

Two women arguing while walking outdoors
A stock photo of two women arguing while walking in a park. Mumsnet user Aeroflot21 has caught her sister in her clothes several times.
AntonioGuillem/iStock/Getty Images Plus

Others believed getting the landlady involved to be a bad idea.

“Assuming your LL isn’t actually your mum, LL is likely to see your relationship as part of the issue here and maybe want you both gone,” said NumberTheory.

“It’ll make you and you sister look like bickering children and if I was your landlord I really couldn’t be a**** with 2 adults who can’t sort something like this out between themselves,” wrote Dicker.

Many users believed the sister is the problem, and that it’s time to stop living together.

“Living with a sister like this is like being stuck in a teen time warp,” said Luredbyapomegranate.

“Maybe it’s time you each had more independence from each other,” wrote Iknowthis1. “Your relationship might be better that way.”

“Your sister has no boundaries where you are concerned,” commented 2Rebecca.

“It’s odd to live in the same lodging if you don’t have a good relationship, and if she steals your stuff and lies about it, that isn’t a good relationship.”

Homedeco said: “If I lived with anyone who stole from me, I would leave and find my own place! I would cut contact with them. I would call the police if necessary.

“She might be your sister, but that doesn’t mean you have to live with her and accept her behaviour.”

Aeroflot21 isn’t the first to ask for help with a difficult sibling online. A man still holding a grudge over his older brother marrying his teen crush was told to “go to therapy,” while a woman was recently praised for telling her “golden child” sister she’d achieved nothing without their parents’ help.

Newsweek was not able to verify the details of the case.