Agreed, although I would naturally expect that she'd be outfitted in nicer clothes as the season goes on, and it would be similarly expected that a hairstylist would be employed to create different looks for different songs. That's just show biz.
But the producers of this show and "American Idol" are not stupid. They wanted you to think that Susan Boyle took them by surprise, and she just might have done so when she originally auditioned. I wouldn't put it past them to have dowdied her up a bit, and that little shimmy move she did before the song didn't seem in character with her life's story. I think it was possible she was coached to do it, as a way of taunting the crowd before wowing them.
The producers of these shows have done the obscurity-to-fame storyline for quite a few years now, and they're still pretty good at selling the same tale with new characters. They know the appetite of an audience for the makeover type of TV show, and they know they have a winner again. Most TV shows work hard to squelch YouTube, etc. broadcasts of portions of shows, these folks have used it as a free marketing campaign. Right now, I'd bet they're making deals with Fox TV to simulcast Susan's next appearance on American TV, and they're lining up sponsors waiting to pay big bucks.
In my case, the only caveat I have is of the most brutal and cruel human lice in Britain; that of the British tabloid press. They have absolutely destroyed ordinary and extra- ordinary people, all because of rumours or spite.
This my only bit of apprehension here.