That was a partition deed orSettlement deed ?
Does the deed clearly sates that the mother and sister want to receive the value of their share of property in cash?
Is it mentioned that the value of property (her share) to your sister is paid by you ?
However if the deed is properly worded and explains everything,besides your sister admits the deed and signed that deed in presence of witness, and if the deed is duly registered then certainly she is only harassing you, and you need not to worry?
You have to prove that you paid bonafiedly the value of her share.
That is why it is always advisble to make the documents in such cases very carefully, it was advisable to get asale deed as you had paid the value of the property.
You have transferred the dcouments and the title of property is in your name now ,while transferring the title of property she signed anywhere?