Isabella was the sister of Abigail Pettigrew. They had Christmas dinner together along with Kazran Sardick and the Eleventh Doctor.
Years later, she pled unsuccessfully with Sardick to release her sister just for Christmas.
Biography from the TARDIS Data Core article, licensed under CC-BY-SA
The Doctor comes down the chimneyThe Doctor falls down a chimney on Christmas eve and meets miserly Kazran Sardick.