Erica was a human woman living in Yorkshire in the early 21st century. She worked as a scientist at Agrofuel Research Operations. (TV: The Pyramid at the End of the World) She was physically distinctive due to being extremely short.
When she was little, Erica wanted to be a bus driver because she liked the way they waved at other bus drivers. At some point she decided to become a scientist and got a job at Agrofuel Research Operations in Yorkshire.
She handed out coffee at her workplace and then proceeded to inspect a project involving plants with her colleague Douglas. When they had to program how much of a chemical agent to spray onto the plants, she asked Douglas to do it. As he had been drinking the night before, his vision was reduced as well. He typed in the decimal point of the number incorrectly and this created an extremely virulent new bacteria unlike anything on Earth.
When they inspected the plants again, they found them turned into dark goop. Once they collected samples of the bacteria, they began evacuating the building. Douglas had already been exposed to the bacteria and Erica watched in horror as it dissolved his body and killed him.
Her colleagues evacuated from the building, Erica was the only scientist who stayed behind to try to stop the bacteria from getting released into the atmosphere by the lab's automatic venting system. The Twelfth Doctor then appeared in the TARDIS. Though they had only just met, Erica was quick to trust him and briefed him on the situation.
The Doctor came up with a plan to blow up the lab, to sterilise the bacteria before it could be released into the atmosphere. Erica helped him construct the bomb and escaped the lab safely, but was unable to help the blind Doctor through the code-locked airlock. (TV: The Pyramid at the End of the World)
Erica got on well with her colleague Douglas and was horrified when he was killed. Nevertheless, she did not let her emotions get the best of her and managed to maintain a calm and level-headed attitude when handling the bacterial breakout by herself. Even after her colleagues had fled, Erica stayed to try to destroy the bacteria, indicating both dedication and bravery. She was also quick to trust the Doctor despite having just met him and even shared humorous exchanges with him to alleviate the stress of their situation. (TV: The Pyramid at the End of the World)