Petronella Osgood's sister

This individual (surname likely Osgood) was the sister of UNIT worker and personal assistant to UNIT Head Kate Stewart, Osgood.

She was, according to Osgood, very pretty, and an icon of jealousy from her sister.

In 2013 when a Zygon copied her appearance the Zygon mocked Osgood for these things as it could see these thoughts in her copied mind and suggested it should have copied her sister instead. Osgood immediately agreed and let the Zygon slip on the scarf she was wearing, grabbed her inhaler and ran away. (TV: The Day of the Doctor)