The husband's responsibility aside, Andrea Yates is severely mentally ill. You can't hold her to the same standards you would a sane person, because she isn't. Sane, that is. As someone said, when she's getting medical treatment, she has enormous remorse for her actions. When she isn't, she's mentally ill again.
If her first trial had false testimony, that's grounds for a new one. Plain and simple. Just like every other American citizen. We don't judge by the standard of whether or not the criminal is sort of OK or really, really bad when we decide to grant a new trial. We use the same standard in each case - and false testimony is one of the reasons a new trial can be granted.
The fact that I personally think Andrea Yates should be punished for the rest of her life for killing her children is immaterial to her getting a new trial.
Sad, sad, sad.