Hey! Of course I know who you are lol Well you will definitely need some watercolour paints (as if that were'nt obvious
) you can get starter kits, or just buy individual tubes of specific colours if you like. tubes are nice because they are easier for mixing, and if you have leftover paint you can just let it dry on your palette, and then put water on it when you are ready to paint again and it will work fine.
As for brushes really you can make do with anything, but art stores generally carry some brushes specifically for watercolour that you can get. Regular brushes will do just fine, as a general rule sable ones are really nice for watercolour, and usually any animal hair ones are better quality than synthetic (although as I said, you can buy a 10 pack of brushes from the dollar store and be totally ok). The main thing is to just take good care of them and they will last a long time. You should also consider getting a hake brush, which are great for doing big washes of colour.
Canvaswise, I think you can buy watercolour boards, but they are probably pretty expensive. I usually buy books or sheets of watercolour paper. You can buy big rolls if you want to cut a specific size, but if you dont need anything extravagant you can just buy a sketchbook of watercolour paper and cut pages out if you want to frame them or anything. The most important thing is getting the right weight for what you are painting. the heavier the paper the wetter you can get it without the paper warping. I would say go with at least 140lb paper, but you can go all the way up to 300lb if you are planning on drenching it.
As for the pen, it looks like a white gel pen, so that might be it. A lot of watercolour painters scratch away paint though, which you can easily do with a dead pen or a toothpick or something while the paint is still wet, which will show the white paper underneath; so that might also be what she is doing.
Hopefully that wasn't too much of an essay
let me know if you have any other questions!!