Ava Curzon is an archaeologist.
She is not a spy, unless you count the fact that her profession sort of spies on the distant past. She wouldn't, especially since when she is first pulled from her 'real life' cataloging items at the Baghdad Museum in war-torn Iraq and dropped into a major mess. She isn't even out in a field excavating anything. All that is true so on the surface you would not consider her an agent in the normal sense.
Curzon sums up her prior history as being "a specialist in the ancient Middle East". She explains, "I studied archaeology and ancient Middle-Eastern languages at Oxford, Cairo, and Harvard. In 2005, I joined the British Museum's Department of the Middle East. In mid-2007, I was seconded to the National Archaeological Museum in Amman, Jordan. In 2009, given my regional experience in the field, I was invited to head up the Iraqi UNESCO taskforce to trace the tens of thousands of artifacts looted from the National Museum of Iraq during the war." She would add that her "published work deals mainly with the countries of this region's fertile crescent. My specialism is the Bronze Age. To most people that means I do the archaeology of the Old Testament period of the Bible."
If, however, you looked a wee bit deeper into her past, not an unusual activity for an archaeologist, you would see quite a different story.
In that one, Ava Curzon is an agent with MI6.
As it states in the dossier that the American DIA has on her and recounts to her in her first recorded adventure, at age 16 she "broke out of your boarding school in England. You found an African tourist company on the Earls Court Road in London, and impressed them so much with your knowledge of east African languages that you talked your way into a job as a tour guide on a Blue Nile Sudan cruise from Sannar. Once they'd flown you there and you'd completed the job, you made your own way cross-country into Ethiopia, back to your family home in Addis Ababa, where your father had been on the British embassy's staff for many years."
After that, the classified record shows, she "followed in [her] father’s footsteps, and that after graduating you worked for a number of years with the British Secret Intelligence Service, MI6". She was the first ever female MI6 officer to work in theater on an operation with the Increment.
Why she left that line of work and went into archaeology is best learned on your own.