Marinette doesn't want to seem rude in not eating the food, so she sits for a moment still and thanks the server, passing them the money.

"Huh? Oh....Well, I might see you at the concert tonight then!" Marinette said, giving a wave. It's only once the girls were gone that she quickly tried a bite of the sundae, not wanting to waste it, before asking for the rest to go. She whispers to Tikki to follow them to check the direction the others were heading in while she waits for the portable take away to carry off with her.

It's a few minutes later before she's able to run out after the girls, carrying the rest in take away options for travel.