What is the ruling regarding the prayer of a grandmother who often forgets during her prayer, prays sitting, sometimes performs one bowing and more than two prostrations, or one bowing and one prostration, knowing that her daughter sometimes reminds her during the prayer, and other times is not beside her?

If the reason your grandmother mixes up the number of bowings (ruku') and prostrations (sujood) is due to the deterioration of her intellect because of old age, then she is not obligated (mukallafah) and will not be held accountable for prayer. This is because the intellect is the basis of religious obligation (takleef), and there is no obligation upon one who has lost their intellect, as the Prophet (peace and blessings be upon him) said: "The pen has been lifted from three: from the sleeper until he awakens, from the child until he reaches maturity, and from the insane person until he regains his sanity."