I agree with you sort of. If you just listen to her words and watch her demeanor without knowing anything else and without trying to make overall sense of her testimony -- she comes across as telling the truth.
And I think much of her testimony is actually truthful. I think other parts are the "truth" as she perceives it; and other parts are flat out fabrication.
That said, when you consider what she is actually saying and try to make sense of it, there are things that don't add up and therefore lend an air of overall lack of credibility to her testimony. It is impossible to tell what's true and what's not, so I think the jury may simply disregard her testimony entirely as lacking credibility.
Furthermore, her testimony has given no indication that Travis was abusive or ever committed any acts of physical or sexual assault against her (or anyone else for that matter), and that is really all that matters for purposes of guilt/innocence.
IMO she and her lawyers all know she will be convicted, and they are simply trying to save her from the death penalty. I've said this before -- the only reason they raised the self defense justification was to allow them to bring in some negative info about Travis. They all know he was not abusive, and they know she does not truly have a self defense case. Their only hope is to try to offset the total brutality and horrific nature of how she killed Travis -- and the only way to do that is to try to make Travis look bad and hope someone feels a little bit sorry for her.