I didn't get into a battle with Ava and was prepared for anything on the first class. I let her wear her dance leotard and didn't get on her case when she wasn't trying the poses. Yes, she was just lying on her mat rather than doing all the poses, but she was listening and she wasn't disruptive. (Meanwhile, Julia was on my back while I was doing poses, but she wasn't disruptive either.)
Once the "Let's Go Swimming" music came on, Ava roused a bit, swimming like a fish in the water. Recognizing the music from last year's creative dance class helped, too.
My assessment: I believe in having kids try many types of fitness, even when they resist. If Ava doesn't want to try another yoga class, I won't insist. Who knows, maybe this will be Julia's thing. She is proudly practicing Downward Dog all by herself at home though she calls it "Underdog."