Here are some of my theories and headcanons (it may be of interest to you)

First, I want to start with Maxwell's quote 

Quote

What year is it out there? Time moves differently here

 
I think Maxwell and Charlie spent over 40,000 years in The Constant. And that is between 1906 and 1910 in earth time. Before Maxwell started taking people from the earth into the Constant. And the first Characters Maxwell Brought into the Constant was Wes, but Maxwell was displeased by Wes poor performance. So Maxwell imprisoned him. This is the list of the Characters that have been Brought into the Constant after Wes. When Maxwell was the king (the list is sorted by order)

Wickerbottom
Wolfgang
Woodie
Webber
Warly
Wigfrid
Willow
Wendy
Wagstaff
WX-78
Winona
Wilson

Now I'm going to explain why Winona is on the list. My reasons are 
1- Charlie did have a split personality when she grabbed Winona (that means it was before she took the throne) 
2- the design of the portal that Winona tried to fix is a bit similar to Maxwell's Door.
So Winona was just on a different island when Maxwell was the king
But when Charlie took the throne. She Brought Winona to the other survivors.

While the Characters in The Constant age normally. The moment they die their age reset to the point they first entered the Constant. But they have the memories of their past lives.

We know that the dark magic and the Nightmare Fuel can change a person's personality a lot like how William turns into Maxwell after finding the Codex Umbra.
When Maxwell and Charlie were dragged into The Constant "they" put Maxwell on the Nightmare Throne and fused Charlie with Nightmare Fuel. That caused her to have a split personality. A side of her was the sweet and caring Charlie. was mad at Maxwell for what happened and the other side was sadistic and cruel enjoyed seeing him suffer on the Nightmare Throne.

Maxwell was worried  about what happen to Charlie but when Wes died of total darkness when Maxwell was watching him. At that point maxwell know that there is a Night Monster, and it is non-other than Charlie. And aside from the split personality she is fully aware and conscious of what she is doing. Charlie relation to the Nightmare Throne is like Webber relation to spiders. The Nightmare Throne is not hostile to Charlie. Since she is not a fully human like Maxwell or Wilson. 

Charlie can free Maxwell from the Nightmare Throne if she wanted to. But if she freed him and took his place. Maxwell may think that maybe Charlie still cares about him. But she doesn't want him to think that way. So she waited and waited. When Maxwell became bored and wanted someone to take his place. While Charlie does have a split personality, she still has a personality. For example, she rolled her eyes every time Wilson died for a silly reason in the Adventure Mode. But finally Wilson took Maxwell place. In less than a minute after that Charlie went to the throne room, and we all know what happens after that.