Frederickson was inducted into the Harvard Society of Fellows in 2006.[5] At Harvard she worked alongside Naomi Pierce on mutually beneficial relationships in ecology. Together they showed that the ways symbiotic host species employ their symbionts is equivalent to the ways employers treat their workers.[6] The process of mutualism involves species such as plants hosting symbionts such as bacteria. Hosts act to reward cooperative symbionts, such as soybean plants directing food toward specific nodules whilst simultaneously killing off those with unhelpful bacteria. Various theories have been proposed to describe such symbioses, including host sanction theory and partner fidelity feedback. Whilst the former describes a scenario in which the host adapts to punish those who cheat and reward those who cooperate,[7] the latter describes a case where the symbionts evolve to try and please the host. Working with an economist, Pierce and Frederickson showed that employment contract theory and mutualisms could be described by similar mathematics.[6]
Frederickson joined the University of Toronto in 2009, where she developed a high-throughput method to better understand the interactions between microbiomes and their hosts. She showed that over time, microbes evolve to develop more beneficial relationships with their hosts.[6][8] She studied the relationships between ants and their hosts,[9][10] showing that ants serve to protect their hosts by monitoring the genes responsible for foraging behaviour. These genes decide how the animal forages for food, and how much benefit the partner plants received. When these genes were activated, the ants recruit more workers to attack herbivores, which ultimately protects plans.[11][12]
In 2019, Frederickson returned to Harvard University as a medical fellow in the Harvard Radcliffe Institute. During her fellowship she worked on a book that explored the concept of mutualism in ecology,[13] and how it can be used to better understand the microbiome.[5][14]
Frederickson has written for The Conversation.[15] During the COVID-19 pandemic, she wrote about how people with caring responsibilities – mainly women – could not simultaneously balance home schooling, online teaching and scientific research.[16]