Is the wife considered sinful for angering her father, who slandered her husband in front of her, due to her defending her husband and his right to care for her?

There is no Shariah violation in a wife defending her husband, and she is not considered excessive in her father's right if he becomes angry, because she did what is legally required. Whoever defends his brother's honor, Allah will keep the Fire away from his face on the Day of Judgment. We hope that her father's prayer against her is not answered, because he prayed unjustly. If she did anything that constitutes disobedience, she must offer sincere repentance, seek her father's forgiveness, and exert effort to appease him and avoid his anger.