A mother has told a court how her five-year-old daughter was killed when her head became trapped in a faulty disability lift at their family home.

Alexys Brown, who was described as a “guardian angel” to her disabled older brother, got into the lift to fetch his mobile phone from upstairs for him. She got her head stuck in a hole in a broken see-through door panel of the lift, and as it moved upwards she became caught between the lift and the ground-floor ceiling.

Her grandmother was unable to operate the lift to free her and called 999. The girl could not be saved and she died at the scene from head and neck injuries.

Alexys’s mother, Lorraine Brown, told Bournemouth crown court on Monday that her son, Jack, who was 11 at the time, had been left traumatised and racked with guilt after watching his sister die at their home in Weymouth, Dorset.

Brown gave a moving victim impact statement at the sentencing hearing of two companies that have been prosecuted for health and safety breaches over a “catalogue of failures” involving the lift.

The court heard that Alexys and Jack were at home with their grandmother, Sheila Green, on 13 August 2015 when he asked his sibling to fetch his phone from upstairs.

Alexys decided to go up in the lift that had been installed at their housing association home. Green was sewing in another room when she heard Jack, who has a neuro-degenerative disease, “hysterically screaming”.

Brown, 33, told the court that her family had been left “broken”. She said: “The heartache and emotion they have had to face of losing their sister and best friend and the circumstances of her death make it impossible. My son Jack had to witness something people wouldn’t even be able to have nightmares about.

“He is receiving treatment for PTSD, he doesn’t sleep or eat. He carries a huge amount of guilt he just cannot let go of. What he witnessed we can only imagine.”

She continued: “We believed Alexys was sent to us for a reason at a time when we were given a horrible diagnosis with Jack. Alexys’ arrival gave Jack something to look forward to. She was and is his guardian angel. She gave him a reason to fight, to be, to live, and that reason has gone, along with his fight.

“Our life is never sleeping due to thousands of ‘What ifs?’ and ‘Why didn’ts?’. The silence is deafening, every day getting worse. As time goes by we just miss her more. We should have been able to protect her and that was taken away from us. It’s just heartbreaking.”

An inspection of the lift carried out by an engineer three months before Alexys was killed identified that there was damage to the door, but nothing was done to fix this, the court heard.

No key was provided, which would have allowed the parents to prevent the lift from being used unsupervised. There was also no emergency handle to allow the lift to be manually raised or lowered if needed.

The lift should have been serviced every six months, but had not had a thorough inspection since January 2012, after an error led the insurance company to believe the lift had been removed, the court heard.

Brown said: “Knowing it could have been prevented turns my upset to anger. Someone failed our family and needs to take responsibility. The world kept moving and ours just stood still. The hurt in our hearts will never end. This is our new normal, hopping through puddles of emotions just to get through the day. Losing a child is beyond grief; there are no words.”

Sara Lawson, prosecuting for the Health and Safety Executive, said: “The catalogue of failures and lack of checks made by these companies led to Alexys’ death. The injuries suffered were horrific. The lift was in an unsatisfactory condition at the time it was in use. If either the hole had not been present or there had been adequate control of the key switch at the time, this incident would not have occurred.

“The systems in place were not rigorous enough and problems with the emergency lowering system had existed since the start of the Brown family’s tenancy and had not been addressed.”

Synergy Housing Limited, a housing association, and Orona Limited, a lift maintenance firm, have admitted charges of failing to discharge their health and safety duty, a breach of the Health and Safety at Work Act 1974.

The hearing continues. The companies are expected to be sentenced on Tuesday.

• This article was amended on 15 January 2019. An earlier version misspelt Orona Limited as Orana Limited. This has been corrected.