Not Literally

 "Sis, you're too fat," the girl said. In her arms, was a woman. And the two were speeding through the countryside at nearly a 100 miles per hour.

"Keep that up and it'll ruin your pretty face," the woman said.

Only the smaller girl was running. She kept panting and groaning and eventually just fell down; luckily there was grass beneath them and so her dress didn't get dirty. The woman in her arms sighed and swirled her finger on the smaller girl's forehead. "I suppose you really were trying your hardest. But just so you know, I'm big, not fat."

She stood six feet tall, weighed about hundred and seventy pounds; to her, she wasn't fat at all. It was just the silver armor which made her seem plush. That two-week long vacation had nothing do with this at all.

As for the smaller girl, she sat down on the grass, sighed a couple of times and, recovered. "Then please run with your own feet and give me a break."

"But we'll be late!"