Hi if anyone can help it would be great

Don't remember much about the book but I think a modern women is either sent back/forward in time and ends up with the H, think hes a leader of some sort, who is off fighting/at war.
Don't think he spends to much time with her in the beginning, so she ends up playing what she thinks is a strategy game most days in one of his rooms, think it might have been holographic maybe, but it turns out to be the actual situations his army/troops are in with the enemy and she is really good at it. h plays a lot of comp games like it back home.
H thinks it is someone else at first, then finds out its the h.
Also remember that they have to go to a sacred temple/cave, the enemy finds them and causes a cave in , think h was inside by herself. Think that's from the same book!!

the strategy game bit was the main part I remembered, hopefully someone knows it, driving me mad!! Think it was a few years ago I read it!
Thanks x