Not every woman can have a perfect “six pack”. It’s one thing to have well developed muscle, but she’d also need to have limited body fat around the midsection to achieve defined abs, and many women simply won’t get there. Not for lack of trying, but simply for want of such fortuitous natural endowment… they ain’t got the right genes for it.
The natural fact is that women are supposed to carry extra fat around their belly area in order to help protect the reproductive organs. Additionally, estrogen in the body gets in the way of fat burning - again, to get the female ready for child bearing. So if you're one of those women who obsesses over obtaining a washboard belly, the first thing you need to do is ascertain whether it’s a realistic goal for yourself.