If I’m understanding you correctly, you have a female character – who is not an MC right now, but a strong secondary character. This character in current WIP is of the Ambassador personality type.
Typically this type is described as:
Ambassadors will be positive about any change and will be highly
aligned, however they will not proactively try to change people’s
points of view. Moving an Ambassador to a Champion will require an
organization to work closely with them, perhaps giving them a part of
the project to lead, which will require them to engage more
proactively. ~ from the http://www.hrzone.com/
Off the top of my head I don’t see any problem with this at all – and there are plenty of historical examples of Ambassadors, who are happy in their position becoming Champions within short time frames, and not only doing well, but thriving.
Truman stepped up from Vice President to President on April 12, 1945, when Roosevelt died. We were still at war with both Germany and Japan at that time. As VP, the role of Ambassador fit Truman perfectly. He was engaged, active, did his job, enjoyed his job and position, and had no designs on becoming president. He rarely discussed world affairs or domestic politics with Roosevelt; he was uninformed about major initiatives relating to the war and the top-secret Manhattan Project, which was about to test the world's first atomic bomb. In fact Stalin knew about the atomic bomb months before Truman did. Truman met with FDR only twice during the 88 days of his VP office.
"Boys, if you ever pray, pray for me now. I don't know if you fellas
ever had a load of hay fall on you, but when they told me what
happened yesterday, I felt like the moon, the stars, and all the
planets had fallen on me."
As a Senator, Truman was fair. He did his job, didn't back down from things he believe were important, such as government spending waste, but it was only after he became president that his background was glorified. At the time though, he was seen as a pure Ambassador type -- both as senator and VP.
Within a week of rise into the White House, he was suddenly an Alpha, and it was only then that people began to see that he had been an Alpha all along.
We have discovered the most terrible bomb in the history of the world.
It may be the fire destruction prophesied in the Euphrates Valley Era,
after Noah and his fabulous Ark". ~ Harry Truman, writing about the
atomic bomb in his diary on July 25, 1945
He demonstrated no sign of insecurity with his new office and massive change of responsibility. For example he asked the current cabinet to remain in place. They understood the situation better than he did, and what the country required was results, not high public impression of him being his own man. He did emphasize a central principle of his administration: he would be the one making decisions, and they were to support him.
He went to FDR's funeral. When the papers tried to make a big deal about this, he told them flatly "He's my friend."
- V-E Day on May 8, 1945, his 61st birthday
- Hiroshima was bombed on August 6
- Nagasaki three days later
- With Japan still slow to surrender, he ordered a massive conventional
air raid on Tokyo for August 13
- August 14th, Japan surrendered
Post war was a mess, and there was havoc every direction you looked. No matter what you thought of his decisions however, you could not say he wasn't a fighter.
So, that is one of 100s of historic examples we could look as a demonstration of this change being well within the scope of the "human experience."
What I would suggest, is that in this book, to give your character an arc which suggests a change – create an event which emotionally drives her into the Champion role. Perhaps something that the current CEO does, or authorizes, results in a catastrophe of some type, which she finds unacceptable (oil spill, gas leak making water flammable, research the Koch Brothers, they have plenty of examples) -- OR -- Perhaps because of an inaction one of her relatives is killed or maimed.
There will be the temptation to do too much with that suggestion -- to get into her head and show details of what is going on. But the way I would play it would be showing the "event" and only mention her in passing. Have her leave the room when the news arrives, taking her cell phone out as she rushes for the elevator -- and that is it.
I suggest this because right now, she is a secondary character. Keep her that way. Then, in the next book, show what happened in her world as a result of that event.
One final comment on this -- the event and her decision to take over, doesn't require her to be a Hero as well as a Champion. Nor do her actions need to be less dangerous or more "good" than the one she has named "atrocity." There are plenty of news stories every day about someone feeling that something is unjust or against God, and then responding to that event with ballistics, explosives, rape, slavery and guns.
Hope this helps.