Simplicity has the official Disney pattern license. I just bought my DD the Merida costume pattern today. It's brand new for this Halloween, and looks great. They also have a new fairy costume pattern that has a very full tulle skirt, kind of like a tutu. There is another style of fairy pattern too, which they've had for a few years, and a Rapunzel pattern as well. The only other official princess dress pattern they have is the Cinderella/Snow White combination pattern your wife probably used the last time.
I ended up search ebay and etsy for vintage patterns for a princess aurora pattern for my DD, since they don't have an officially licensed one any more.
The Simplicity patterns are available at pretty much every fabric store, and they go on sale for $1 or 99 cents every few weeks!
McCalls and Simplicity also have several knock-off patterns if you're looking for other characters like Alice and Tiana. They're not exact, but they're pretty dang close.
Happy sewing!
(And I'm sure that the fabric stores in Canada have the simplicity patterns. If not, you can order them at simplicity.com, but they're more expensive that way.)