I love those, especially the first one you posted.
I'm not sure how she does it, but it looks like the tulle is cut in a random sort of way and scrunched up possibly? That might not hold shape forever though, even the cheap stuff I have used from UB will straighten back out if it becomes wrinkled (which it really, really does lol). It could be singed as another person said, which would hold the wrinkles permanently. I have no extra tulle to play with so I can't experiment right now but those are really nice! Might just have to get a bit of tulle when I run to HL tonight and give it a try.