She is not the world's greatest singer for sure, and the part directly after the break at about 2mins.40 just plain sucks. But most of the song itself is OK, as long as you don't compare her vocal abilities to Don's. The video to the studio version is one of those cheap 'sex sells' shots.
I prefer her live version anyway, cause at least she DOES sing live (Did you hear that, Ms. Spears? Women are allowed to sing live!).
She overdoes the posing a bit, too - but I guess it's tough to go on a stage with 'Presley' as your last name. Without that name she wouldn't make it onto TV, but she could front a cover band playing clubs and bars, like many others, too.