Jraven, I took a deep, deep breath having read your post. I loathe the Spice Girls phenomenon and the effect their existance seems to have spawned throughout popular culture, particularly on little girls, hence the new (in my humble opinion) hideous creation of "tweenagers" (little girls obsessed with makeup/clothes/boys/popgroups and very little else). Thank goodness my eleven year old seems to have just missed this latest gimmick in marketing.
However, I digress, as I said, I loathe the packaged stereotyped presentation of the Spice Girls (and such like)and the images they project of women and for sometime battled against it. They were at the height of their success when my daughter was eight and however much one tried one could not avoid them. Eventually I relaxed about it rationalising that my daughter has a very balanced up bringing was very aware of the Spice Girls marketed image and despite them being everywhere she did always have my constant refrain expressing a different perspective!
No one was more surprised to find themselves at one of their concerts than me. It was an excrutiating experience but it was the only time I have ever indulged my daughter and given in to something I really, really objected to. (Largely because I felt that it was good for both of us to take on board the fact that we are different people who often like diffent things and besides, how can I preach tolerance if I am not prepared to show tolerance?)
I do think that an eight year old worrying about her weight is alarming and it seems that this age group is being targeted more and more by magazines, tv, pop groups etc., to look and be a certain way. In fact I find the whole thing quite horrendous. However, now eleven my daughter grew out of the Spice Girls some time ago, and she now considers them as being slightly ridiculous. Perhaps this is widespread as their last album was a complete flop(?)... I think the only thing that you can do for your niece is give her a healthy, broader perspective on the whole issue. Force feeding her a counter opinion will not help (she will inevitably rebel against it). Healthy discussion and the daily awareness that those she looks up to (such as yourself) are not obsessed with the things that the spice girls (and many others) appear to stand for, is the best, and most unconscious, education she can have. Good luck...