Ana Kosara was originally an Ekaterina, but she later joined the Madrigals after passing the Madrigal test with flying colors. Because of many things that happened during the time she was a Madrigal, she became a Vesper. She only joined the Madrigals so she could spy on them and to give an advantage to the Vespers. She has a relative named Teodora Kosara, who is also a Vesper and Ekaterina.
"The branch leadership was thrilled to grant Ana Kosara Madrigal Status. A teacher, a political activist, and a member of the Ekaterina Branch, Ana passed the Madrigal test with flying colors. The Madrigal leaders were particularly impressed with her efforts to fund orphanages in her native Bulgaria. However, soon after Ana joined the branch, strange things started happening. Top secret documents disappeared. Madrigal agents were unable to complete simple missions. It was as if the other branches knew their plans ahead of time. The leadership launched an investigation and made a shocking discovery. Ana was an imposter. Her Cahill lineage was real, but her qualifications were not. She had lied about her teaching experience. She had faked the orphanages. It was all part of a plan to infiltrate the Madrigal on behalf of the Vespers--a secret organization that has been trying to sabotage the Cahills for the past five hundred years. Ana was expelled and the Madrigals drastically changed their screening process, but the damage was done."