[@Sailorsadie]

That would probably be difficult as the Red Kind is the brother to the White Queen and we have a good reason in place as to why there are two Kingdoms to begin with. 
[list]
[*]It is possible for the Queen of Hearts to be a third and separate power on her own, wanting the rest of Wonderland for herself and deciding to join the war. 

[*]It is possible that the Red King and her had a relationship that went sour and he banished her so she is very much against him more than the White Queen.

[*]It is possible that the Queen of Hearts supports the Red King, hoping he will find the Alices secret to traveling worlds and leave Wonderland which means one less rival.

[*]It is possible to have the Queen of Hearts actually be the Red Kings wife.
[/list]
These are all just possibilities I can think of off the top of my head and even I know that a few probably won't work as it will lock the other person's background in place before they even join. As it is, the Red King is the sibling to the White Queen. That is the only thing locked into place. The background or how they view their childhood could still be very different as they are only Siblings related by marriage. This means they still have freedom and my not even view the White Queen as a sibling. 

The reason why the Queen of Hearts being related to the Red King might be hard is that, right now, they don't have a background that is too locked into place. While, if you add a [i]real[/i] sibling....that changes things.

You are more than welcome to follow the sibling idea if you can show me a very convincing character that will not lock the Red King's background to into place as I want to give the roleplayer as much freedom as possible.