This is the exact strategy that I imposed and it worked tremendously (albeit, not exactly how it was supposed to). I had gotten a 750 on my Math SAT without even studying for it and was now planning to study for Math very strongly, get an 800, and move onto studying for my Writing/Reading score which was not nearly as good. Somehow I only improved 10 on Math but then improved by 110 points on Writing/Reading. I think the strategy works very well though.
@Zinhead This strategy does include working on your weaker section, but it simply puts it off and tries to get your stronger section up to its highest and then you can solely focus on your weakest section.
If she really is very strong at Math there is also a possibility that all that Math studying could stick with her and she could score her highest on the one she prepared for Writing/Reading without even preparing for Math. Everyone is different but I really liked this strategy. There is a point where she will have to focus on this “scary section” though, and she will have to be truly committed to improving if she is going to see some improvements.