The correct legal position is as follows.
Since your grandfather had passed away leaving behind a will, your father and uncle become absolute owners as a result of that will. you have mentioned a proper partition has taken place between your uncle family and your father.
The owners of this property are 1) your father 2) your uncles family.
your sister has no right in this property as your father is alive and it is wrong to call this property ancestral property. your father has every right to do whatever he wishes to do with his share of the property.
The legal solution to your problem is to seek evictment of your sister through court. Only issue is that , if you appraoch courts it may take some time until an eviction order is passed. The best solution is to explain to her that she has no right in the property and a fair share will be given to her after you complete the construction.