Her magic turn her body into water and water I'd formless, what she did is either a form change similar to takeover or a requip
Lol then why did she chant the spell like lucy
She said she just wanted to be a mermaid because jealousy over Lucy, i believe she beat him entirely by outsmarting the enemy and with her own powers
there is a panel there she said, she kinda hope lucy was there so they could power up by performing unison raid with lucy's aquarius, since they already did that when fighting vivaldus at TOH . I guess a part of that making juvia come up the idea of casting aquarius key by turning herself a mermaid (juvia-aquarius) so she kinda felt that her power increased bcoz of the thought lucy performing unison raid with her again. thats why she called it " power of love and jealousy". Nevertheless, thats juvia's idea and power all alone. ヾ(☆▽☆)
So DID she use celestial magic for a second or just part of her water magic