KendixPL, I'd have to say that she was ineffective with Azula due to Ozai's overriding influence on their daughter. Azula's power, intelligence, and personality required a firmer hand in her upbringing. Ursa tried to be that firm hand, but Ozai rewarded Azula's manipulative, domineering, and aggressive personality. And with him being the only person strong enough to contain her, it made Azula virtually fearless of her mother and rendered Ursa's attempts to better parent Azula and give her the love and the discipline she needed to develop a less malignant personality ultimately futile.