Is it permissible to spend a perpetual charity (Sadaqa Jariyah) on a surgical operation for a 32-year-old female cancer patient who is a widow with a child?

Continuous charity is an endowment (waqf). Giving charity to this woman does not fall under continuous charity, but it is a great good deed for which the doer will be rewarded. It is permissible to use zakat funds for her medical expenses as long as she is in need and has no one to support her.