I thought the S option was only a couple grand?
It's definitely worth it unless she doesn't care about performance at all.
Also, they're redesigning it next year and it is going to have way more power,
so you might want to make her hold off,
at least until the end of the MY to get a good deal,
or until the new one comes out.
edit: the standard Mini Cooper is getting a hp bump from 115 to 150hp and they are supposed to come out Summer 2006 as a 2007 MY