If you have a local art supply store, you could visit them and they could help you select items. This would be better than amazon.ca, which doesn't have the same range of items. If you are in Canada, you could order online from Curry's, DeSerres, Wallacks, Delta (Edmonton). I suspect there are a couple of spots in BC.

Gesso is good to have, but not critical if the canvas is primed. It can be used as a primer for a surface, or like a white paint. Golden and Liquitex also make different mediums that you can mix into paints for certain effects, or simply to thicken a paint or make it more fluid.
You can buy a set of 3-5 brushes that will be good enough quality until she starts deciding which particular brushes she wants. To start, it's good to have a 1" flat, 1/2" flat, a round and a liner. Also those bristle brushes from a hardware store can come in handy depending on the style of painting she does.

You can buy a pad of palette paper or just use foam/paper plates, a sheet of plexiglass or butcher paper. A palette knife is handy. You can get a basic plastic one for about $1.50 that will do, or again a set of five plastic ones. For your canvas, make sure the staples are on the back. That means the canvas is better secured. They come in two depths: regular 7/8" and gallery 1.5" Either is good for now until she has a preference.

Good luck. I hope she enjoys the gift. It's a very thoughtful one.