Depp has firmly denied ever physically abusing Heard.
According to Ms Henriquez, she "begged" Heard not to marry the Pirates Of The Caribbean star, who she claims was "verbally abusive, even when he was sober" and often used derogatory terms towards her sister, including"f***ing ugly c**t" and "fat wh**e".
"He could insult her and say he loved her in the same sentence, with equal amounts of passion," she told the court.
"I remember him often saying 'f***ing ugly c**t, you fat wh**e … but god I f***ing love you" – and things like this."
Ms Henriquez also claimed Heard and Depp's relationship was "tumultuous from the start" and that she'd spotted "signs of physical abuse – including cuts and bruises" on her sister early on.
As a result, she said she "tried to intervene" and told Heard to break up with Depp, but to no avail – and that she'd "felt sick" when she'd found out they were engaged in September 2013.
"I told her it was a bad idea, begged her not to go through with it and said that she should end it because it wasn't going to get better," Ms Henriquez said.
"I asked her, 'Why are you putting up with this?' – and told her that him putting a ring on her finger was not going to stop him hitting her."
In 2014, Ms Henriquez began living rent-free in one of Depp's luxurious Los Angeles apartments just two doors down from the actor and Heard, but was kicked out after being wrongly accused of selling photos of her sister and Depp's wedding.
During the trial, she admitted she was aware of the alleged abuse when she moved into the ritzy building.
"You certainly would not have lived in the next-door penthouse apartment for a period of one year if for one moment you thought that what was going on in the next-door apartment was your sister (was being hit by Depp)?" one of his lawyers, Eleanor Laws, asked her.
Ms Henriquez replied, "It was happening and I chose to live there."
She added that she'd begun confronting Depp about his alleged physical abuse of Heard for the first time in 2014, but he'd "flat out deny it".
"Sometimes he would flat out deny it or downplay it by saying, 'No, I just pushed her, I didn't hit her,'" Ms Henriquez said.
"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 p***y,' and would say, 'Sis, I just lost control.'"
Ms Henriquez went on to detail a disturbing event in late 2015, in which she claims to have gone to Heard's home and seen "blonde hair and blood" stuck to a splinter on the bed frame.
"I remember imagining what kind of force it would take to do that because it was such a heavy and solid frame," she told the court.
She also alleged Depp once turned physical towards her, and almost pushed her down the stairs during a fit of rage towards her sister at his LA home in 2015.
"I remember being worried that I was near the edge of the top of the stairs. When he got to the top of the stairs, he was pulling me backwards so he could get to Amber," Ms Henriquez said.
"I remember being scared because I was worried that I would fall backwards and fall down the stairs.
"Johnny reached out to shove me out of the way to lunge at Amber – reaching out to try hit Amber – and instead struck me, hitting me in the arm.
"Amber suddenly lurched forward and hit him and said, 'Don't hit my sister.' I didn't see exactly how Amber hit him but it didn't seem especially hard; it was just enough for him to lose momentum.
"She was just trying to protect me and I think it probably stopped me from being pushed down the stairs.
"There was a struggle with me stuck in the middle of it, and he really went for Amber.
"Somehow I was pushed out of the way so I wasn't between them, but I was standing right there next to them when 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."
Earlier this week, Heard also spoke about the alleged incident, claiming she'd stepped in to protect her sister and remembering a "rumour" of Depp throwing ex-girlfriend Kate Moss down a set of stairs.
Moss and Depp dated in the 1990s when she was 20 and he was 31. Depp has denied hitting her while they were together.
"I did strike Johnny that day in defence of my sister. He was about to push her down the stairs," Heard told the court this week.
"The moment before that happened, I remembered information I had heard (that) he pushed a former girlfriend – I believe it was Kate Moss – down the stairs," she said.
"I had heard this rumour from two people and it was fresh in my mind.
"In a flash I reacted in defence of her.
"For years, Johnny's punched (me) and for years I had never even hit him. I never so much as landed a blow and I will never forget this incident … it was the first time after all these years (I hit him back)," she said.
Heard and Depp were together from 2011 to 2016 after meeting on the set of The Rum Diary. Their divorce was finalised in 2017.
Depp has vehemently denied any physical abuse and claims Heard was abusive towards him. She alleges he threatened to kill her and abused her through punching, slapping and kicking her as well as controlling her finances and behaviour.
Depp has branded Heard's allegations "complete lies".
