Is it obligatory to give money to the poor female head of household, for whom we had donated to build a house in the desert, after she refused to build and requested money instead, claiming she was moving to the city, with the fear that she might squander the money?

The fundamental principle for funds collected for a specific purpose is that they should only be used for that purpose. If a person dies, becomes financially independent, or the purpose ceases to exist, the funds must be returned to the donors.

Thus, if money was collected to build a house in a rural area, and then the beneficiaries changed their mind about building and decided to move to the city, the money should not be given to them unless the donors are consulted and their approval is obtained. If the donors agree to give them the money to help them rent a house, then it is their decision. If they decide to spend it on something else, there is no objection.