What is the ruling on paying Zakat for the past year, given uncertainty about whether it was paid, and a significant portion of the money was spent on operations? Is it permissible to pay Zakat in Rajab? And is Zakat to be paid on the value of the money before or after it was spent?

If the sister is unsure about having paid the Zakat (definition) on her money for last year, she must pay it based on the amount of money at the time the Hawl (the passing of one Hijri year) was completed, not on its current amount, because it is a debt upon her. There is no preferred month for paying Zakat; rather, it must be paid immediately upon the completion of the Hawl, and it is not permissible to delay it except for a valid excuse or an overriding benefit. Money spent during the Hawl is not subject to Zakat after the Hawl has completed; rather, Zakat is due on what remains of it, if it reaches the Nisab (definition).