if the defense was able to get just one juror to have doubt about her guilt on murder charges then that's enough to declare her not guilty. in fact, that's the entire basis of our judicial system when it comes to criminal court. all 12 jurors must agree on the charges or else it doesn't hold up.

i know from (second-hand) experience that a murder conviction in a case built on circumstantial evidence is incredibly difficult to achieve. this is why many cases get reduced to manslaughter, but even then they weren't able to convince the entire jury of her guilt on manslaughter charges either. this tells me that the defense had just enough evidence to convince at least one person of the jury that she might not have done it, which is all they had to do.