What is the religious ruling on a mother's estrangement from her daughter, and her refusal to maintain kinship ties and communicate with her and her grandchildren for 21 years without a valid reason?

If a mother abandons her daughter without a valid reason, she has committed the grave sin of severing kinship ties and neglecting her daughter's right. However, the mother's abandonment does not justify the daughter reciprocating in kind. Rather, it is incumbent upon the daughter to strive to maintain ties with her mother and show her kindness, in accordance with the Prophet's (peace be upon him) saying: "The one who maintains ties of kinship is not the one who reciprocates, but the one who maintains ties even when his relatives sever them," and his saying: "If you are as you have said, then it is as if you are feeding them hot ashes, and you will continue to have a supporter from Allah against them as long as you persist in that."