Is the questioner considered disobedient to her mother and sinful due to her shortcomings in caring for her, even though she visits her daily and serves her, while her mother constantly complains about her daughter's lack of attention?

You are not disobedient to your mother, and there is no sin upon you. Strive to treat your mother with kindness and please her as much as possible, provided it does not conflict with your duties towards your husband and your home. Old age is often associated with irritability and quick temper, hence the texts of the Qur'an and Sunnah have particularly emphasized the necessity of patience with parents in this condition. Allah the Almighty says: "And your Lord has decreed that you worship none but Him. And to parents, show goodness. If one of them or both of them attain old age in your life, say not to them a word of disrespect, nor repel them, but address them with gracious words." And the Prophet (peace be upon him) said: "May his nose be rubbed in the dust, then may his nose be rubbed in the dust, then may his nose be rubbed in the dust." It was said: "Who, O Messenger of Allah?" He said: "He who reaches old age with either one or both of his parents and does not enter Paradise."