Ruling on leaving the fast of a vow due to the excuse of illness

Question:
We received a message from Bisha, from the sender (S. M. J), who says: A woman vowed that if her child is healed from the illness he suffered from, she would fast three days every month for the rest of her life. What is obligatory for her today after she has fasted as much as Allah willed of this vow, then she was afflicted with an illness, and she is now the mother of five children, unable to fast and fulfill the vow.
We ask for clarification. May Allah reward you with good.

Answer:
The Prophet (peace and blessings be upon him) said: Al-Bukhari recorded it in his Sahih.
And Allah praised those who fulfill their vows, saying -Exalted and Majestic is He-: [Al-Insan:7] And this is among the characteristics of the righteous, and the righteous servants of Allah.
So it is obligatory for her to fulfill her vow; because fasting three days of every month is an act of nearness and obedience, and the Messenger (peace and blessings be upon him) encouraged it and made it desirable. So if she vowed it, it is obligatory for her to perform it when the condition is met. So if Allah heals her sick one, it is obligatory for her to fulfill the vow. And if she is unable in some months due to an illness that afflicted her, she makes up what is made up of Ramadan; she makes up the three days from another month when she is well. And if she is completely unable at the end of her life, then she feeds a poor person for each day, like Ramadan, as if she were unable to fast Ramadan, she feeds a poor person for each day. So these three days, if she is unable to fast them due to old age, she does what she does in the fasting of Ramadan. Yes.