Pratibha belongs to the erstwhile royal family of Keonthal state, who consider this seat as a safe bet where the polls are due on May 7.
Her rival Ram Swaroop Sharma of BJP is reaching out to voters with the appeal of being a comman man.
"Congress has been playing a key role in the development of Himachal Pradesh and the country and we are asking vote on the development plank," she said, addressing a rally, spelling out the developments initiated in the constituency, considered the second largest in the country after Barmer.
It includes the tribal-dominated assembly constituencies of Kinnaur, Lahaul and Spiti and Bhermour.
Pratibha had won the Mandi parliamentary seat bypoll last year by defeating Jai Ram Thakur of BJP.
"We will ensure that her victory margin is more than last time when she defeated her nearest rival by over 1.30 lakh votes in the last by-election to the seat," a local Congress leader said in the rally which was also attended by the Chief Minister.