9th Daughter claiming share of property patitioned in 1975-76

Hello, My grandfather have 4 sons and 5 daughters. The 9th daughter is claiming share of 1/9th now. She issued us 2 notices recently. I tried finding partition deed, but failed to trace it as it looks like those days this system of paper work was not present and I understand it is a oral family settlement between male family members. My father the 6th one for my grandfather got all the 4 of his sisters married, among those the last women is claiming share as my uncle's (1st son) children are selling some portion of property as they landed up in heavy business losses and loans. Because they are getting compensation and land values have gone up in recent times, she is thinking of moving to court for resettlment. Other facts of the matter 1. 9th daughter born in 1972 2. Family partition happened between1975-76 3. Grandfather died in 1978 4. Agricultural property 5. Subdivision and land passbooks, revenue records are all showing the entries of 4 brothers in equal shares. 6. No daughters claimed any prorties except the last daughter 7. My great grandfather purchased the whole property and he distributed to his 3 sons, one of them is my grand father 8. I have EC showing my dad and my 3 uncle names and their shares 9. AP meebhoomi website also showing names of these 4 brothers in 1B, Adangal 10. We have land passbook issued by Govt of AP - Pattadar Passbook 11. Subdivision form copy is with us. I need advise on whether we should reply to her via legal notice If she goes to court on what grounds we could challenge the case. Thanks