Ke$ha may have a wider frame, but she is VERY fit. There is no spillage like Gaga. Even in Gaga's extremely tacky and tastless V magazine cover shoot, you see her fat rolling from the top of her hips. She can't help that (she actually could help that, if she worked out correctly). Ke$ha on the hand has a very TIGHT, very FIT body. Very much a gymnast body.
And that's due to Ke$ha eating and exercising correctly, unlike Lady Gaga, who probably does, no lie, coke or some other drugs combined with not eating and little exercise to get "her body back." That's why she fluctuates in weight, and that's probably why her hips gave out due to her constant unhealthy behaviour. But whatever works for you, chick.