No, it is not ancestral. Your sister has no concept of what an ancestral property is. She has no share in the property seeing as it was willed to your father, then to you and your mother and finally to you. At each step of the way, it continued to be self-acquired property of the individuals concerned.
The concept of ancestral property has gone a drastic shift post 1956 with the enactment of the Hindu Succession Act. An ancestral property is only that property that has remained with the male line of a family through inheritance for at least the past four generations—son, father, grandfather and great-grandfather. The moment there is a partition, it ceases to be ancestral property. On death of a coparcener, for example, there is an automatic partition and the share of the deceased coparcener devolves upon their heirs as self-acquired property. Self-acquired property can become ancestral property by way of blending or (where there is no pre-existing HUF) by creation of an HUF and transfer of that property to that HUF.
The long and short of it is that property inherited through a will is not ancestral property.
Further queries are welcome. Have a nice day!