She knows that she will scream and roar. When that happens, she will produce a lot of flames that will contaminate the crime scene. She definitely doesn't want that, so she kept her mouth shut.
What they had found in Stella's apartment was the worst thing that she expected to have happened when Black Widow didn't show up. Be that as it may, it was what she was mostly expecting because there have been many such cases recently.
Many heroes have died because of the secret war between them and villains. So she was expecting it. But she didn't like it.
She thought to herself, "I caused all of these. It is my fault that so many good people are dead. If only I hadn't started the war, so many people would have lived."
She thought she was thinking in her head, but she had actually been muttering audibly for everyone to hear. What she said made the other four look at her. But only one of them came forward to console her.