Sangma, who defeated National People's Party Phillipole Marak in the June 27 by-election in Chokpot constituency in South Garo Hills district, is the fifth women legislator in the assembly.
Chief Minister Mukul Sangma and his cabinet colleagues besides senior government officials attended the swearing in ceremony at the conference hall of the assembly secretariat.
Bluebell, who is a first time legislator, said her priority would be to address backwardness in her constituency which indirectly fans militancy.
"My priority will be to take up the matter related to the deteriorating law and order situation in the entire Garo Hills region. I hope I can contribute to uplifting the economic condition of the people," she said.