The ruling on the prayer of one who does not know the correct method of prayer

Question:
My grandmother is a woman who performs much worship, but her prayer is not valid. I have tried to correct her, but she says: “I learned from so-and-so and so-and-so.” What is the ruling on her prayer?

Answer:
Try to correct with her what she has gotten wrong, to the extent of your ability, if you are well-informed about what you mentioned and you know Allah’s ruling in what you mentioned. Try to advise her and explain to her what she has gotten wrong. For example, if she does not recite Surat al-Fatihah, teach her; if she does not recite the tashahhud (testifications), teach her; and if she hurries in the ruku' (bowing) and sujud (prostration), teach her. Tell her: “This action of yours is not sufficient for you.” Read to her the hadiths of the Messenger of Allah (peace and blessings be upon him) until she is reassured and until she understands and comprehends.