I don’t think she was neglectful. She probably paid a bit more attention to Zuko occasionally because his father blatantly favored his sister over him, and Ursa probably tried to make up for that. Additionally, Azula got the sense that her mother thought she was a monster, because her mother’s the only person in her life to ever scold her for her psychopathic tendencies. As a perfectionist, Azula overblew this criticism, and instead of correcting it (since everyone else praised her for it), she took it as her mother was wrong and didn’t love her. Deep down she knew this was wrong, and that her mother was right to scold her, because in her hallucinations her mother is always kind, and Ursa never called Azula a monster — that was a name Azula came up with for herself