The mother of the murdered teenager Brianna Ghey has said the under-16s should be banned from social media, describing it as “an absolute cesspit”.

Esther Ghey was speaking at a screening of an ITV documentary that explores the murder of her 16-year-old daughter by two schoolchildren.

In the programme, which is to be broadcast on Thursday, Ghey travels to the US and speaks to an insider who tells her people are “defenceless” against the algorithms of social media companies.

Brianna was killed by Scarlett Jenkinson and Eddie Ratcliffe, who were both 15 at the time and had attended the same school as her. On 11 February 2023 they lured Brianna to a park in Cheshire where she was stabbed 28 times with a hunting knife.

Both were jailed for life with a minimum term of 22 years for Jenkinson and 20 years for Ratcliffe. The court heard the killers were partly motivated by Brianna’s transgender identity.

The 75-minute documentary celebrates Brianna’s life and features interviews with three of her friends, who describe the schoolgirl as kind, chatty and funny. It also explores her death and issues around online safety.

Brianna, who had thousands of followers on TikTok, struggled with her mental health, which was worsened by accessing eating disorder and self-harm content on X.

From the age of 14, one of her killers, Jenkinson, enjoyed watching videos of real killing and torture on the dark web, fantasised about murder and developed an interest in serial killers.

At a screening in London, Ghey said one of the reasons she had chosen to take part in the documentary was to “get answers” from social media companies about safety.

Last year, Australia passed a law aiming to ban under-16s from social media. Ghey said she supported such a ban.

“It is an absolute cesspit,” she said of social media. “Even if, say, I do an interview, and I’ll try not to look at comments, but I can never help myself, and I’ll look at the comments, and you’ll see people saying about my child, trying to tell me what gender my child was, and also really, really horrific comments too.

“When you report things, the support isn’t there.”

Ghey added: “I’ve reported so many comments, and I always get the response that they haven’t done anything wrong, that it’s not something that they can take down, and our children have access to those comments.

“No matter how much love and compassion you pump into your child when you’re bringing them up, and how much empathy you can teach them, they will go online and they’ll see the way that other people are speaking about other people and they might think that that’s right.”

In the documentary, Ghey meets Arturo Béjar, a former engineering director at Meta, who testified before Congress about child safety on the tech company’s platforms. He tells her that people are “defenceless” against harmful algorithms.

At the screening Ghey expressed hope that any social media company would not put “lives before profit”.

Ghey founded Peace & Mind UK to raise funds to teach mindfulness in schools. Her recently published memoir on her and Brianna’s lives, which explores how deadly social media can be, was described by the Guardian’s Simon Hattenstone as “one of the most unflinching, inspirational autobiographies I’ve read, a remarkable cry of hope from the depths of despair”.

Meta, X and TikTok have been contacted for comment.