Osgood was a scientist who worked for UNIT when Kate Stewart was in charge and was also her daughter. On the Eleventh Doctor's orders, she analysed the stone dust in the undergallery under the National Gallery. She was asthmatic, and often forgot to use her inhaler when she needed to, often when over-excited. The Zygon who took her form disliked this and was annoyed at "getting one with a defect," and promptly took her inhaler. She had a sister (TV: The Day of the Doctor) and a brother (HOMEVID: downtime)
Behind The Scenes
It is currently unknown whether this Osgood is related to the UNIT soldier Tom Osgood seen in TV: The Daemons.