Is it permissible to pay back a debt to one's mother with an amount less than what was previously agreed upon, especially with the change in currency value, particularly since the mother refuses to accept the debt and demands a larger amount, citing the change in currency value, even though she lives with the questioner who covers her expenses?

If the questioner's daughter built on top of her mother's house, then either she donated the construction, in which case she is entitled to nothing from the sale price, or her mother gifted her the upper part of the house to build and own, in which case the price is divided according to the value of each floor. What the questioner took and gave to her mother is not sound. The correct position is that her mother is entitled to the value of the ground floor at the time of sale and in the currency in which it was sold. The new house that the questioner bought belongs solely to her. The mother's maintenance is obligatory upon her affluent children if she is poor, and desirable if she is rich, and it is permissible to ask the sisters to participate.