We have to judge people by the standards of the societies they live in and the context, as unpalatable as it sometimes is. Washington, who fought for freedom, was a Slave Owner. If he were alive today, he wouldn't be. When the Japanese surrendered at the end of World War II, Kantaro Suzuki was allowed to continue serving as Prime Minister, even though he'd been a leader in the Axis of Evil. Harry Truman dropped an atomic bomb on Hiroshima and Nagasaki. He's arguably (I want to stress I said "arguably") a mass-murderder. FDR rounded up Japanese-Americans and put them in Internment Camps. So these leaders who we uphold as great leaders weren't exactly what I'd consider pure.
Mirror Georgiou was born into a culture where killing was how you advance. She was probably born into the elite and knew of no other way to live. If she lived in the Prime Universe, that's probably not what she would've done or how she would've behaved. Prime Georgiou is proof of that. Anything she did in the Mirror Universe is within the jurisdiction of that Universe and whatever she might've done could be classified as military actions in whatever wars she was fighting and anything she did was legal within the jurisdiction of her society and universe.
If Georgiou commits any crimes in the Federation or acts against Section 31 or Starfleet, then that changes everything. So far, she hasn't done that.