Sir she legally your sister has share and further there is not relinquishment deed done by her. So in general there is no defence, further your father died in December 2005 that is after amendment so even it is ancestral property she gets a share.
So in this case what would i suggest would be you and uncle offer her some amount and take a relinquishment deed on settlement. or take lame defences and continue suit for 10- 12 years there is no other way further the defences can be made by perusing the plaint filed by her,