Hugo sat on his bed thinking about what she said, so, that was her past? Her uncle was the reason why her mum got bitten by zombies. And that's why she had a certain kind of behavior according to what she said. Remember, she was an apathetic kind of person before she started mingling with Hugo.
Mingling with Hugo changed her, that's the fact. So, this was the reason why she possessed that ugly character in the past? Though she still possessed another bit of ugly character now...over-confidence. But it wasn't that much though. And according to what she said, though she didn't complete the statement, if she gets hold of him, she'll kill him.
Does she have the mind to do so? To kill someone? Well, who knows. From the anger he heard in her voice while making that statement, she'll most likely do it. He wanted to talk to her, he wanted to know more of that story, but he couldn't...it was late in the night.