How can one deal with a mother who does not appreciate her daughter's sacrifices and causes marital disputes, especially after the death of the father upon whom the daughter relied?

It is obligatory upon you to be dutiful to your mother. However, the husband's right takes precedence over hers when there is a conflict. Therefore, you are not permitted to stay overnight at your mother's house without your husband's permission. Caring for her is an obligation upon all her children. You must balance being dutiful to your mother with fulfilling your husband's right, and be dutiful to her to the best of your ability. You should strive to appease her and speak kindly to her, and seek help from Allah.