Queen of Cards - Trade Rule Differences
When the Queen of Cards is in your region the way that the Trade Rule works completely changes. It will no longer degenerate (and stick) which means that whatever the Queen of Cards is set as will remain your Trade Rule throughout the region until she leaves.
Sometimes you'll challenge someone to a game of cards and their Trade Rule will be "One", just cancel and challenge them again. It'll go back to what it was. This is actually known as Trade Rule degeneration which has caused much confusion in FF8. Many people think using the All Trade Rule is a bad idea because it degenerates into Diff which is false on two accounts.
First is, all Trade Rules degenerate into One, they don't degenerate in a stair-like fashion as many people claim. This is easily observable too. Second reason it's false is because when the Queen of Cards is in a region there is no Trade Rule degeneration. If the Trade Rule reverts back to One, just challenge the person until it goes back to All. It's as simple as that.
You can take advantage of how the Queen of Cards works (and many people do) by moving her location to someplace where you want to win cards or play cards. In order to move the Queen of Cards to a new region you have to lose a Rare Card to her.
There's plenty of useless Rare Cards so this shouldn't be too big a deal. Plus if you're smart and Save + Reset if she doesn't go where you want then it'll only cost you one Rare Card per move and you can control where she moves. (You can also win back any Rare Card you lose to her by playing her brother/son in Dollet. He's the kid involved in the Dollet Artist Quest).
For the majority of the game you're going to want to keep the Queen of Cards in Balamb and Dollet. In order to do the Queen of Cards Side Quest she has to either be in Dollet or move to Dollet, otherwise she won't give her father the Rare Card you lost to her.
Key - Current Region: New Regions
Balamb: Galbadia (62.5%) and Dollet (37.5%)
Dollet: Galbadia (62.5%) and Balamb (37.5%)
Galbadia: FH (62.5%), Balamb (12.5%), Dollet (12.5%) and Centra (12.5%)
Centra: Dollet (37.5%), Galbadia (37.5%) and FH (25%)
FH: Esthar (62.5%), Winhill (25%) and Dollet (12.5%)
Trabia: Dollet (50%), Balamb (25%) and Lunar (25%)
Esthar: Lunar (50%), Trabia (25%), Dollet (12.5%) and FH (12.5%)
Lunar: Can move anywhere in the game & no hint is given to where she is going
On Disc 3 you will most likely want to move the Queen of Cards to the Lunar region since the Card Club Group (involved in the CC Group Side Quest) is the best source for Rare Card farming at the end of the game. On Disc 4 they will be using Lunar rules instead of Balambs.
That's really about it for the Queen of Cards and using her Trade Rule to your benefit in Triple Triad.