—first: the money is not lawful for you if it was obtained in the manner we have described—by deception and lies—and therefore you do not rightfully own it. What you must do is return it to its source and rid yourself of it.
However, if you received it legitimately—meaning you were actually enrolled and continuing in your studies—and some cash accumulated with you, and it reached the nisab (the minimum taxable threshold), which is the value of fifty-six Saudi riyals in silver or its equivalent in paper currency, or more, and a full lunar year has passed over it, then zakah is due on it at the rate of one-quarter of one-tenth, that is, two and a half per cent. Allah, Exalted is He, knows best.
Question: What if the payments she receives from Social Security are not conditional upon her being a student, and the letter from the school is taken only as an address or a means of identification?
Answer: If the allowance is being given to her by Social Security because she is poor and in need, then there is no objection to that. But she stated that she is studying and that the payment is not released until a certificate from the school is presented; this indicates that she is receiving it as a study stipend. If that is the case, it is not permissible. If, on the other hand, it is disbursed to her as assistance for the needy and poor—like the support given to orphans, minors, widows, and the like—then the money is her property, and once a lunar year has passed over it and it has reached the nisab, she must pay zakah on it.