Wow, you made her face look so elegant yet you still didn't take the look of a child away from it. Great job with that! Her curls are quite beautiful. The soft highlights you used makes you hair look natural and very playful. Also, great job with the bubbles. You made them pretty realistic looking and they look awesome! Beautiful job!
Bubbles Z is my favorite of the Z versions. She's so cute and cheerful <3 (and, although I'm hardly an extreme expert on either series, I get the impression she's been butchered less than Blossom Z or Buttercup Z XD). Admittedly, this drawing looks a tad less cheerful (more like she's having a rare "serious moment") but still adorable in its own right.
Very well drawn, too. And the bubbles (the... actual... bubble bubbles) are gorgeous, as well.