At some point before her accident, Kathleen slept with her husband's brother.
Hospitalization and DeathEdit
Kathleen was struck by bits of a shattered baseball bat after the machine became jammed and the bat shattered. In addition to puncture wounds, she had a Colles' fracture, which was set in the ER. During the surgery, April Kepner cut her clavicle in order to access and stop some bleeding in the area. Despite Callie's best efforts, Kathleen had a stroke due to a clot that formed because Kathleen had an unknown coagulation disorder and she couldn't save Kathleen's life and she died on the table.
Following the surgery, Leah was prepared to tell Dante about the affair. However, Callie stepped in before she could say it and told Dante that Kathleen had said that she loved him.
Kathleen was married to Dante Kane until her death.
While married to Dante, she cheated on him with his brother, Marcus.