It's how I plan to have female protagonist option in my project. As an expansion after it's finished. Totally different character on the other side of the story.
One core element of my concept is two "factions" competing against each other, so while the male MC tells what happens on one side, the female MC would be from the other.
However, to get *cough* back to your game, I agree that changing Kelly into a second protagonist would too much work. This is something that would need to be planned early to make the best of it, in my opinion. But, I like your approach just as much, as it still will be distinct enough from the male option to warrant a playthrough or 100.