Okay:
Tilan Siana was born on Bajor in the year 2341, close to the middle of the Cardassian Occupation of the planet. Watching her people beaten everyday as well as seeing her family begin to splinter took its toll on her, causing her to grow a tough outer skin and remain impassive, letting no emotions show in public. With both her parents in the Resistance, it wasn't long until she was brought in as well, at age 17,. From 2358 until the end of the Occupation (2369) Siana was busy with helping coordinate and plan strikes against Cardassian targets, the most significant of which was her attack on the Central Communications Building in Ashalla. During this same time, she became the unofficial head medical officer as well, coordinating relief efforts (when possible) and traveling around Bajor surreptitiously and at great risk helping to treat the wounded, dying, and ill . Although skeptical of the Provisional Government, especially after the Circle Incident and Starfleet, especially with Starfleet's role in using the former Cardassian seat of power, Terok Nor, as their base of operations in the Bajor System, she accepted the rank of Field Colonel with the Militia, and acted as the "Surgeon General" until Bajor's admittance to the Federation in 2376, when the majority of the Militia got absorbed into Starfleet. After a brief time at Starfleet Academy, most of it spent in getting up-to-date medical knowledge, using Federation technology, and Federation surgical and medical procedures, not to mention adjusting to that way of life, Siana was offered many different assignments, including a position as Assistant Head of Starfleet Medical, Non-Human Department. Feeling adventurous for the first time in her life, she requested to be assigned to the U.S.S Armstrong, a Challenger-class starship, which spent most of its time dealing with the Tholians and Selelvians for the first four years of her service, after which it underwent an extensive survey of the Badlands, followed by trail blazing in the closest areas of the Perseus Arm. Between and after these exploration missions, the Armstrong dealt with typical Starfleet missions, most of which required Siana's medical expertise.
This is what I managed to flesh out so far for the CMO character.