It doesn't matter how fat someone is, she's training the girls and its working. The pressure to look good onstage isn't there anymore for her to keep in shape and that was the case for many of my professors and teachers once they got older. The girls can dance exceptionally well for their age. That kind of training works.
That being said, watching this show makes me really glad I never started training at a competition studio. They make it all about winning trophys when that's not what its about. The use of her pyramid to rank the girls every week is gross and doesn't do anything but crush their self esteem. They cry almost every episode because the fights between the moms and its all captured on camera. That can't be good for an 8 year old.