How should one ideally deal with a mother who speaks inappropriately and causes problems when advised, and is it considered filial impiety to hurt her feelings when attempting to guide her?

Your duty is to address your mother with respect, reverence, and gentleness. It is impermissible to mistreat her or speak harshly to her, even if she commits a wrongful act. In such a case, you should forbid her from it gently and respectfully, without harshness or abuse.

Allah (the Most High) says: "So do not say to them, 'uff,' and do not repel them but speak to them a noble word. And lower to them the wing of humility out of mercy and say, 'My Lord, have mercy upon them as they nurtured me when I was small.'"

If the mother becomes angry, do not press her further and leave her, for enjoining good and forbidding evil with parents is not like with others.