Is it permissible to take the usurious interest amount as compensation for the depreciation of the currency, knowing the dire need for money, and that the principal amount is the value of a land that has tripled while the currency's value has fallen to less than a third?

The basic principle is that money should be returned as it is, and it is not permissible to demand an increase on it, as that would be usury (riba). However, if the currency has depreciated by one-third or more, and the debtor was an usurper or a procrastinator, then he is obligated to compensate for the damage. The amount is estimated based on what it would have been worth in a stable currency, such as the dollar, and is now paid in a currency other than the original one to avoid the appearance of usury.

If you verbally or in writing relinquished your right and absolved the deceased, then you cannot go back and demand it. However, if you forgave her for her injustice towards you through procrastination or not returning the money, without absolving her, then you can demand it, because absolution is only concluded verbally, in writing, or by what carries their meaning.