Amber Heard sometimes had bruises and burns on her arm as well as marks on her face during her four-year relationship with Johnny Depp, her younger sister has told the high court in London.

Whitney Henriquez said tDepp was “incredibly jealous and possessive” and would get “paranoid”, often smashing or destroying Heard’s mobile. “She was constantly getting new phones because Johnny would trash [them].”

Depp, 57, is suing the Sun’s publisher, News Group Newspapers, and its executive editor, Dan Wootton, over an article that called the Pirates of the Caribbean actor a “wife beater” and referred to “overwhelming evidence” that he had attacked Heard. Depp denies ever hitting Heard, 34, who has submitted details of 14 occasions during their relationship when she claims he assaulted her.

Henriquez, who lived for a year beside the couple in one of the Los Angeles penthouses Depp owned, said in a statement that the relationship had been tumultuous “from the very start”, although she had not initially been aware of any violence.

“He really didn’t like her working and this got worse the longer they were together … Johnny was incredibly jealous and possessive.”

Henriquez said she began to notice “signs of physical abuse, like bruises or cuts or burns on her arm – and this was early on”. She told the court: “She always had an excuse: she had bumped into this or that, or she had a mark on her arm from burning herself while cooking or using her curling iron for her hair.”

Later Henriquez said: “I saw that her face was swollen and she had a mark under her eye. I had my suspicions before, but it was clear to me that she had been hit. She admitted to me that he had hit her, but at that time she was constantly … blaming herself: she said that she must have done something to annoy him or antagonise him.”

Henriquez believed Depp’s drinking and drug use affected his memory. “He would talk about blacking out, but he could also convince himself about how things went down and you couldn’t convince him otherwise. Amber sometimes recorded conversations with Johnny to be able to show him when he was sober what actually happened.”

Henriquez said she confronted Depp on occasions. “Sometimes he would flat-out deny it or downplay it by saying: ‘No, I just pushed her, I didn’t hit her’ Other times, he would acknowledge that he had hit her but would try to justify it by claiming she hit him first, or ‘she called me a pussy’, and would say: ‘Sis, I just lost control.’”

Henriquez said on one occasion, on a staircase in the LA penthouses, “Johnny grabbed her by the hair with one hand and I saw him punch her really hard in the head with his other hand multiple times.”

Eleanor Laws QC, representing Depp, questioned Henriquez’s account, saying Depp had been wearing a bright green plaster cast on the hand he allegedly used. Henriquez said that was indeed her recollection.

Earlier Heard completed giving evidence. Texts she had sent to her mother, Paige, describing Depp as “nuts”, “violent” and a “madman”, were read out. They had been sent, Heard said, after Depp “refused to leave the breakfast room at his LA home … He wanted me to admit that I was having an affair with my ex-partner [Tasya van Ree] and another gentleman I barely knew.

“He had done cocaine and drink for well over a day, for about 36 hours, and at the time I was unfamiliar with his patterns.”

Heard sent a text to her mother: “It’s terrible, Mum, I don’t know what to do. He’s nuts, Mum, violent and crazy. I’m heartbroken that this is who I love.” Later she sent another text: “It’s OK. He’s not being violent to me. The crazy mood swings and hard to handle.”

Asked by Sasha Wass, QC, representing News Group, whether she had been telling the truth, Heard said she had not told her mother about all the attacks. “I was trying to talk to someone who might know how it felt,” she said. She added: “My father was violent to my mother … and they really loved each other.”

In a subsequent text, Heard told her mother: “I feel really lost and lonely. He’s a madman. I feel I’m on a fastening train but I don’t want to jump off. I stay on the train even though I know it’s about to explode.”

Ending her evidence, Heard said she had appeared in court because “every day more and more attacks were coming out accusing me of being a liar”. Asked by Wass what the benefit was of speaking out, Heard said: “What woman has ever benefited from being the victim of domestic violence in her own story?”

The hearing continues.