From what I got, she doesn't seem to be invested in her testimony or her importance in the case. Perhaps that's the result of her being scared or immature, but I don't think that's what's significant. The defense has done a pretty good of baiting her into appearing to be an inconsistent person. A witness admitting to lying is not a good thing; I don't really buy the whole she admitted to lying about certain things, she couldn't be lying at all. It's a shame that her flaws are going to affect the case, but I think that's going to happen.
Is Zimmerman actually going to testify though? He's not obligated to. See about 4:00 minutes into the video.
This is an important point.
I, for one, find it pretty odd that she didn't try and contact someone when this all went down. And I think the defense figures that there are members of the jury that will distrust her or dislike her for not stepping forward right after the tragic event. That doesn't necessarily mean she's lying about anything but it demonstrates that she's somewhat unreliable and not too strong of a person. That'll hurt her credibility.