1) Since your father has executed a registered Gift deed in your favour that too in the year 2007, your sister cannot make any claims now and you are the absolute owner of the property in accordance to facts and law.
2) No need for a sale deed as suggested by your friend as in your case, it is your father's self acquired property which he has gifted to his son.
3) The points that will validate your title vide the Gift deed are :
a) That you have demolished the old house and constructed a new 2 storey structure after obtaining building permission from government authorities(GHMC/Panchayat) as applicable.
b) That you have done improvements to the property by constructing a new 2 storied structure by availing bank loan and by investing your own funds.
c) Your sister who got married in the year 2001 cannot claim ignorance of facts because invariably she would have been a witness to the demolition or the construction of 2 storied structure approximately between 2007 to 2012.
d) That the electricity bills and property tax receipts in your name since the year 2007.
e) You have availed bank loan and the property has been mortgaged to the bank.
4) Since your father was the original allottee in housing board corporation and subsequently he Gifted this property to you, the nature of property will be self acquired property only. Your sister cannot claim it as ancestral property.
5) Law of limitation will strictly apply to your case- It is close to 6 years between the Year of Gift deed and your father's demise. If at all the Gift was to be revoked by your father, your father should have ideally revoked the Gift by 2009. Since he did not revoke the Gift till the time of his demise , the gift is valid .
6) Law of limitation will strictly apply to your sister's claim: Your sister cannot challenge Gift deed now as it is close to 9 years and hence even his children (your sister) cannot question the gift made in the year 2007.
7) Your sister does not have any right on the property as your father has executed a legally valid registered gift deed in your favour when he was alive.
.Hope this helps