Wow! Nice game! The graphics (especially the MC) is beautiful, the level are well thought out and polished, the controls are smooth, the final sequence is satisfying. And there is the extra optional challenge rooms too. That's quite some flourish that you seldom see. Good job!
For a bit of nitpick I'd say the timing of the gem dash is a bit unclear, probably need some more visuals to that. The jump is a little bit floaty, which is okay for me, but do feels a bit punishing when you see the character slowing floating do to her doom, which is just sad. Sometimes I mistook the background as a platform and died a few time, which felt a bit cheated.
But these are just small things anyway, you've done a very good job in making this game! Well done!