The three kids who bought the melon juice earlier were the catalyst for more people to start crowding their little stalls. Even Princess Margaux is very much in the know regarding crowds and yet she didn't expect to feel suffocated by all the people trying to buy from their little shop.
Julia is working double time by peeling watermelons at a fast speed before putting them inside the tank jar and blending them inside using her manipulation of the water and easily crushing all of the flesh of the watermelon. Since it didn't have any seeds, she didn't need to segregate them all and just crushed everything inside the tank in one go.
As for Elaina, she is already so experienced in handling crowds that the crowd that is currently waiting for their orders is nothing to her. She continues to serve the people with a smile on her face, and a threatening and scary face the moment a few thugs tried their chance at intimidating her.