Apologetics and low expectation bigotry.
She's in a court of law, she should have the respect for the court that demands she not use her local dialect to communicate to the broad society. Most rational people who have been raised in any sense of the term properly, meaning respectful of others, realizes that this is the problem, not that she speaks ebonics as a primary language in her personal life.
I cuss all the time, shit, fuck, damn, etc. plus slang. I wouldn't use that language in a courtroom, however. That's the problem. She didn't have the sense to realize that there are appropriate and inappropriate places to behave, and speak, the way she did, and that was a sign of her low caliber character and bad upbringing, which goes to her character, which undermines her testimony in so far as it diverges from the other known evidence in the case.