Mayka Kukucova has insisted she "never wanted to hurt" millionaire Andrew Bush when he returned to his house with his new girlfriend in April 2014, but acted in self-defence.
The 26-year-old, a Slovakian swimwear model, told the courtroom in Malaga she had gone to the property to collect her things when he unexpectedly turned up.
She said: "When he came and saw me he told his girlfriend (Maria Korotaeva) to go out to the car.
"He started shouting and hitting me and took me strongly by the arms. I said I wanted to go but he said no.
"He was shouting that he was going to kill me and my family."
The prosecution says Mr Bush died after being shot three times - once in the shoulder and twice in the head.
Kukucova told the jury the gun had gone off after a struggle down the stairs, and said she did not know how many times it had been fired.
"I couldn't hear anything. I was just trying to get away. I didn't want to hurt him," she added.
Carlos Larranaga, defending Kukucova, confirmed during the proceedings that his client had shot Mr Bush, but added: "There was a homicide but we have not accepted that my client is a murderer.
"You must decide if Mr Bush was killed in an aggressive way, or as a method of defence."
Kukucova handed herself in to police in her hometown of Nova Bosaca in Slovakia four days after the shooting, and was extradited to Spain to face charges of murder and vehicle theft.
She has not submitted a plea in relation to killing the 48-year-old.
Mr Bush owned a jewellery store in Bristol before he moved to the Costa del Sol, and his sister and niece were in court.
Ms Korotaeva, who met Mr Bush while studying as an undergraduate at the University of West England, also attended the hearing.
Following his death, she wrote on Instagram: "I will always love you. You will always be in my heart. The man who changed the world for the better. My teacher. I wish I could of saved you. RIP Andy Bush."
The trial continues, and is expected to last until the end of the week.
