Possibly machine appliqué, or else fabric paint. Think of each pose as your block, and then you can do interesting things with other fabrics in between the blocks. I'd look at traditional Indian art as well as chakra colour schemes for inspiration.
In terms of picking the yoga poses, decide how many you want to put up and then ask your daughter which ones she'd like, as there are loads of yoga poses out there and no doubt she has several pet ones. Or perhaps a standard sequence, such as the Salute to the Sun?
I know very little about yoga, I'm sure other people can suggest more, but I'll be watching this with interest.