Honestly, I say go for it! I don't really know how the S100FS acts, but i have a s9600 and it is much better than the s5700. Besides, the Velvia & Provia looks the S100FS can emulate is a great feature heavily asked for by photographers who miss these films. The aperture again is a great plus for the S100FS, 2.8 will blur background elements more. As far for the s9600 I cannot use the Super Macro feature on anything except the widerange(28mm) so, for extremely close shots she will have to be extremely close
. Hope this helps!