Is it permissible for the monthly sums sent to a needy widow to be disbursed from Zakat funds?

If the amounts sent to the lady were not intended as zakat, then it is not permissible to count them as such, because the intention must accompany the disbursement of zakat. The amounts sent are considered charity for which the sender will be rewarded. As for the future, it is permissible to give her from zakat if she is poor or needy and has no one to spend on her, because zakat is given to the eight categories mentioned in the Almighty's saying: "Indeed, [prescribed] charitable donations are only to be given to the poor, the needy, those employed to collect [zakat], those whose hearts are to be reconciled [to Islam], for [freeing] captives, for those in debt, for Allah’s cause, and for the stranded traveller; [this is] an obligation from Allah. And Allah is All-Knowing, All-Wise." Also, zakat must be promptly disbursed when it becomes due, unless there is an excuse.