What is the ruling concerning the prayer of my mother who does not recite the Fatiha completely, nor a surah after it, nor does she complete the Tashahhud, given that she is illiterate and 68 years old?

The worshiper is not required to recite anything while standing except for Al-Fatihah. Anything beyond that is a Sunnah (recommended). It is obligatory for a mukallaf (a person legally competent in Islamic law) to learn Al-Fatihah and the Tashahhud, as the prayer is not valid without them. If one is unable to learn them after making an effort, then they must recite what they can from them, and their prayer will be valid thereafter, based on Allah's saying: "So fear Allah as much as you are able" and "Allah does not burden a soul beyond its capacity."