Just some random thoughts about art classes:

I was a precocious artist as a child, almost totally self-taught. I was given this book as a gift when I was maybe 8 and I highly recommend that for an artist of that age who shows talent: http://www.amazon.com/Drawing-Right-Side-Brain-Definitive/dp/1585429201

One time in maybe second grade we had an art teacher come to our class at school to show us how to draw flowers. Long straight stick for a stem, symmetrical leaves on each side, a U with some points for a tulip blossom. Done! To this day I don't draw flowers any other way, and I think that's the worst sort of way to teach a child to draw. It wasn't until I took a drawing class for my art degree at a university that I was actually taught how to really look at something and translate that to paper when drawing from life.

For a 3-year-old, though, you'll want to let her have fun exploring different types of media. I haven't reviewed all of these sites thoroughly but you may find some of them helpful:

http://www.mrsbrownart.com/index.htm

http://www.kinderart.com/

http://www.lz95.net/mw/talbert/stugal.htm

http://www.crayola.com/lesson-plans/