Scream is a symbiote spawn of Venom and an enemy of Spider-Man.
Donna became a security guard for the Life Foundation. As part of their program to create a super-powered security force, the Life Foundation scientist merged the resulting creatures with five of their most skilled and trusted employees. One of those employees was Donna. She fled back to the Life Foundation's base in the Mojave Desert. Spider-Man stowed away on her hovercraft and released Brock. Diego and the other new symbiotes lost the resulting battle, and they apparently died from accelerated aging when Brock used a metabolic accelerator on them. Her symbiote was turned into dust and her body caught in a massive explosion.
It was later revealed that Donna left with their immature symbiotes and hoped that Brock would work with them so as to teach them control. Brock refused and Diego had a psychotic episode and went wild in Times Square. She succeeded in drawing the attention of Brock and Reilly. Brock fought with Diego, and only the intervention of Reilly saved her.
The other "guardian" symbiotes took him to Chicago. He managed to escape. Brock reunited with Venom before Diego could kill him as well and defeated her. Diego somehow gained a measure of control over her symbiote, or at least reached a modus vivendi with it. To make up for her past behavior, she began seeking out other symbiotes and helping their human hosts to cope. She soon learned of an alien called Xenophage that preyed on symbiotes. With Brock's help she defeated it.
In Diego's most recent appearance, she found the Xenophage's ship. Along with Brock and Wolverine, she traveled to an alien dimension and returned safely to Earth.
Donna Diego met her demise in a most void manner: while investigating the murder of Scott Washington (a deceased host to Symbiote Hybrid), she was lured into a trap by obsessed and Symbiote-less Eddie Brock, who got brainwashed by a villain named Crime Master into hating everything Symbiotes, went on hunting of Symbiotes. Using a sonic emitter, he paralyzed her and slew her with a heated dagger. It was a thankless end for a woman who was beginning to learn to be a heroine.
Scream was one of the five Life Foundation Symbiotes that were forcefully spawned from the Venom symbiote. Unlike her "brothers", she wasn't merged into the Hybrid symbiote, being still at large at the time.