Juror number 10 says "how can you believe him, knowing what he is? I lived among them my whole life. You can't believe a word they say" what does this tell us about your number 10

Number 10 is stuck in the past and has probably been a victim of some issue and cannot comprehend the idea that people can change.  

Explanation:

Why did they even pick this juror if the juror is prejudice against the person she is referring to?  She should have never had the option to be a part of a jury that she has already determined someone is guilty without hearing the evidence.