Is it permissible for me to contribute to the building of a mosque in another country to fulfill a vow I made to build and furnish a mosque, given my difficult financial circumstances after graduation and my preoccupation with repaying debts and covering family expenses?

A vow of obedience contingent upon a condition becomes binding when that condition is met. Since the questioner vowed to build and furnish a mosque if she graduated, she is obligated to fulfill this vow. Building the mosque is not restricted to a specific country, unless the questioner limited her vow to that effect. If her intention was to build an independent mosque, then contributing to a mosque's construction is not sufficient, unless she specified a certain amount at the time of the vow and that amount is not enough to build a mosque. If she did not specify a certain amount, then she is obligated to build a mosque. If she is temporarily unable, the vow remains her responsibility. If her inability is permanent and unlikely to be overcome, then she should contribute to building a mosque with whatever she can, and offer the expiation for breaking an oath (kaffarat yameen).