Cofelia travelled across the galaxy to find obesity on a great scale, which led her to Earth. Disguised as a human, she headed Adipose Industries, which produced a drug that claimed to attract human fat cells and flush them. In reality, the pill attracted the fat and transformed it into an Adipose body. However, this was deemed illegal by the Shadow Proclamation. Seeding a level 5 planet, such as Earth, was against Galactic Law. Circa 2009, she activated her drug, using the power of the molecules in human bodies that were supposed to make the people lose weight.
After the Adipose young were galvanised, they removed themselves from human flesh and waited to be collected by Cofelia. When the Tenth Doctor interfered with her plans, she was stopped from killing one million humans in the birth of one million Adipose. Instead, they all survived and the March of the Adipose had only ten thousand young.
A nursery ship arrived and beamed the Adipose on board, but the First Family knew what they were doing was illegal. They chose to rid themselves of their accomplice, Cofelia. After the Adipose were beamed up, the Doctor and Donna tried to persuade Cofelia to get away when she was in the beam. However, she did not listen. Eventually, the beam switched off and she fell to her death. (TV: Partners in Crime)
At all times, the Matron remained very calm, even when being arrogant or cruel. Cofelia looked threatened when the Doctor warned her about possible consequences to her actions, but retained her poise. She was very proud of her profession as nanny to the Adipose, and seemed to care about the Adipose. In the end, Matron Cofelia's arrogance and pride betrayed her when she was killed by her employers.