Is the questioner considered sinful or blameworthy if he does not prevent his aunt from wasting water, knowing that she wastes excessively, causing the water bill to rise, and his wife and mother avoid advising her to avoid her negative reactions?

Extravagance in Wudu (ablution) and Ghusl (ritual bath) is disliked (makrooh). The Prophet, peace and blessings be upon him, said to Sa'd, "What is this extravagance?" He asked, "Is there extravagance in Wudu?" He replied, "Yes, even if you are on a flowing river."

Therefore, you should inform your paternal aunt and explain to her the ruling of the Sharia with gentleness and kindness. Invite her to economize in water and gradually show her the correct method for Wudu and Ghusl, without reprimand or harshness, especially if that would lead to a greater harm. If you are unable and she does not respond, then there is no sin upon you, and you are not obligated to denounce her in a way that leads to a greater harm.