This is Lazuli happily showing off her own Quartzeon form to Zhina.
Of course, she learned how to transform into a Quartzeon form because of her sister becoming one and she wanted to mimic her.
The difference between the two is that both of them are based on different elements. Zhina managed to evolve into a darkness inspired Quartzeon after her Dark Gem reacted with electromagnetic energy and she gained strength because of her training. Lazuli modeled her Quartzeon form based off a Psychic Gem and because of the fact that she's naturally a Mew, so it's a bit of a hint at her true nature, to some degree.
