widow of slain bell gardens mayor lyvette crespo pleaded not guilty and was ordered held on $ 150,000 bond .
the 43-year-old told authorities it was in self-defense after her husband punched their teenage son when he tried to intervene in the fight .
her former brother-in-law claims that allegations of years of abuse are all a lie and says he has text messages proving the slaying was in cold blood .
crespo faces up to 21 years in state prison if convicted .