Witness testimony is well known to be poor. We've known that for quite some time.
That doesn't mean it's always incorrect or useless. There are more than 2 options. While it can be poor, sometimes it can lead to an arrest.
The point is, this person was simply not a witness at all.
Yet, she made a valiant attempt to be vocal in the media to try and persuade public opinion. Hence, she needed to be proven wrong in front of the Grand Jury to give the full story. You know, the exact same way the Brown supporters did with the media. They lied to make their "side" look innocent and victimized.
She wasn't there. She wasn't listening. She simply repeated what she had read after events had already occured. That's not a witness. Even giving that witnesses' memories are flawed, she's not a witness at all. Now please stop humiliating yourself.

Where did those goalposts go? Whether she was there or not, no one is giving her testimony credence. Care to guess why? Because the prosecutor made it clear to the Grand Jury that she was full of ****.
Now, let's take your criteria and put it against the pro-Brown witnesses. What's seriously pathetic is that they WERE there, some even saw parts of the event, and instead of giving honest statements to the press, they lied. They consciously made the decision to make up a fake tale of the events, all to make Wilson look as if he committed a crime. They repeated stories that were told around the neighborhood after the events had taken place. Sound familiar? Yeah, it's the same exact thing you said about this lady. If you want evidence, you should do something you've failed to do up to this point, and read the transcripts from the Grand Jury. The pro-Brown witnesses say it, they admit to it. It's not something that can be contested.
Again, you conveniently ignore the truth to rationalize your confirmation bias. Double thumbs up!
It's quite remarkable how far you'll go to co-sign brazen corruption.
CAN YOU HEAR ME ON YOUR HIGH HORSE? MUMBLES? CAN YOU HEAR ME? Please.
ETA: Wait, are you seriously trying to argue that this is okay, since the prosecutors argued unethically on both sides!?
No, I'm saying that the prosecutor was justified in showing that both sides lied to the media in order to give themselves a better image. She had a job to do, and that was to present the information to the Grand Jury in it's entirety so that people wouldn't cry foul. Low and behold, for some people it's still not good enough.