It's not, she is just not slim. What people refer to as stubborn belly fat, outside of those who have lost 100s of pounds, is really just them being at a high bodyfat % and not knowing it because most people wouldn't think to get a dexa scan. I don't feel like watching that video above but in general you can't spot target fat loss, and your stomach is typically the last place you will see reductions in the size of the fat cells.
You can spot target fat with a surgeon though.